It took place as an IM discussion so that's how I'll post it.
Him: O_o why are there tracks to a place that doesn't exist?
Him: The train to the arctic north. Canada doesn't even have trains that go that far north. And we love trains!
me: Perhaps Celestia foresaw such an eventuality?
Him: Probably, she's pretty amazingly powerful and stuff.
me: And yet she needs 6 young ponies to solve crises? I know, I know: she's grooming them to be her successors.
Him: I have no idea if that's what's going on there. She's setting Twi up for something, but part of me wants to believe that simple succession is too obvious.
(A pause in conversation occurs while I read something he emailed titled "A Mostly Accurate Summary of the History of Equestria" where he references Celestia and Luna finding the Elements of Harmony.)
me: Hm, that's something I'd not thought of. I had always assumed that Celestia had CRAFTED the Elements of Harmony. But wouldn't it be a kick if they existed before her?
Him: She actually said that she and Luna found them before facing down Discord.
me: Huh, I missed that. Which is interesting, because the EoH are, presently, optimized for 6. So either there are 4 alicorn princesses who are missing,
the EoH are some degree of sentient and can re-configure themselves.
Him: Given that both Luna and Celestia are a thousand years old and don't look a day over 30, I'm pretty sure that they're probably kind of special.
me: No doubt, but I recall Twi asking why Cel and Luna couldn't defeat Discord again, like the last time, and Cel said something to the effect of "The Elements are keyed to you now." As in "They picked you"
Him: I would think of it as Celestia and Luna both having the Use Magic Item ability that 3e rogues had which let them emulate the appropriate factors to activate the elements, and because they're like level 40 bad-asses they can do it to 3 or even all 6 elements at once.
me: But that again begs the question, why have the Mane 6 fight Discord?
Him: Once the true vessels of Harmony were revealed, the EoH went from "Eh, you'll do" to "NO ONE BUT THE CHOSEN ONES"
me: So you're positing a divine destiny sort of thing.
Him: I actually honestly think that Celestia is surprised at the power of the Elements even though she used them before.
me: So the 6 aren't just exemplars, but avatars?
Him: I've always had that position. I kind of think the harnesses and crown are just foci anyway, and the real element is the ponies themselves. Kind of like the Dragon Scroll in Kung-fu Panda... the secret ingredient is that they're awesome.
me: Assuming this is true -- and I'm not necessarily disagreeing with you -- this means that all of Twi's existence has basically been a Xanatos Gambit by Celestia, because what are the odds that 5 of the 6 Avatars of Harmony are living in Ponyville? Ergo, Celestia must have one hell of an intelligence network**, manipulating things such that all the avatars are in one handy place for her Chosen One.
Him: I say fate.
me: If you say fate, then Celestia is either incompetent or a gambler of such a level that she needs counseling. "Yes, all the prophecies indicate that my evil and immensely-powerful sister is going to escape and imprison me. I shall do fuck-all about it, except to send my student to Podunk Town in the hopes she figures out what to do in time." Sorry dude, I just don't buy that.
Him: I'm not sure that Celestia even knows what the ultimate purpose of the Elements really is. It's possible they exist for one specific task that will be the end of them.
Him: Well, it needs work. And actually, that four lost alicorn princesses thing kind of makes me think that the four lights that entered the moon in Mare in the Moon might have more significance.
me: ..... ooh. There's definitely plot potential there. If you'll pardon the pun.
Him: Why would Celestia and Luna never mention these other Alicorns? Are they possibly Alicorn princes instead? Why would they wait 1000 years if they always intended to free Nightmare Moon? If they didn't intend to free her, what changed their minds?
me: Damn, I like the way your mind works. Actually, let's go 3 princes and another princess, so there are an even number. Well, odd number really. But a MATCHING number.
Him: I like that. I have this sinister plot in my head but every way I try to work it, there's no reason to suppress the knowledge of other Alicorns that doesn't also throw Nightmare Moon under the bus - except Celestia's regret.
me: Make them like the Ringwraiths? Corrupted by Nightmare Moon's power, they became... VAMPONIES! Dun dun dunnnnnn!
Him: Essentially the other alicorns betray Celestia (who is an utter paragon of Harmony) and try to throw her for a loop by corrupting Luna, clearly not expecting that Celestia would place the good of Equestria before the good of her sister, but if they're, essentially, the previous bearers of the Elements, how does Celestia use the Elements against Nightmare Moon? With all five of the bearers turned against her, how could she activate the magic?
me: I dunno, but here's a thought: What if Sombra was an alicorn? We don't see much of his body. His wings might be hidden under armor or robes or whatever.
Him I was just thinking that!
me:Which... oh shit. OK, hang on... Cadence is an alicorn, whose cutie mark is a crystal heart, and now she lives in the Crystal Empire. Clearly, Cadence is Sombra's heir! IT ALL MAKES SENSE!
Him: My brain has exploded
me: MINE TOO!
Him: Okay, so I was just thinking, isn't Chrysalis also an Alicorn of a sort?
me: Yes, of a sort. Which reminds of something I saw on My Little Brony. Let me dig it up... Aha! http://cheezburger.com/6990634240
Him: Oh my! Wait, wait... did Chrysalis maybe get a hold of Sombra and that's why his heart was black? Because she ate all his love?
me: Possibly! Or maybe Sombra used the love poison on her and it turned her evil.
Him: I'm... not quite getting the logic jump in this picture... or was Sombra trying to make Equestria unappetizing so Chrysalis would go somewhere else? And actually, if that's the case then those two things aren't incompatable either. Though he had no love, he still had a duty.
me: AHA! http://i.imgur.com/BU3JMoY.png
Him: +1,000,000 internets
me: AND LOOK THE PRINCESS IN THE ILLUSTRATION IS AN ALICORN.
Him: "The book states that a long time ago, an Earth prince had given an Alicorn princess the drink intending for it to make her fall in love with him. However, they were so lost in each other's eyes, they were unable to perform their duties, and their kingdom fell into ruin." Sombra is not an earth pony... unless that horn of his is something going horribly wrong.
me: OK. So someone else corrputed Chrysalis. Fair enough. And she tried to seduce Sombra, so he turned all dark. It still works, it's just less romantically tragic.
Him: There must be fallen kingdoms all over Equestria by now O_O
me: It fits the genre.
Him: I think that both Chrysalis and Sombra will make a return. Oh... maybe that's why Celestia wanted to reform Discord? So that there would be some extra muscle for when they eventually did return!
me: Makes sense!
Him: I'd really like to see Discord in the background of a few episodes, maybe with other ponies, so that we know he's making friends.
me: Okay. WOW. Good work.
Him: Wait, there's the Alicorn amulet. Where did that come from?
me: Good question.
Him: It honestly seems kind of evil
me: There were theories it was Sombra's, and there's the chance his horn flew away in the explosion.
Him: His horn totally flew away. I remember thinking "That horn kind of didn't even seem to be damaged apart from the fact that it was no longer attached to a unicorn." Which... if the alicorn amulet works on anypony and not just unicorns, your tragic romance is back on.
me: And that reinforces my "Sombra is an alicorn" hypothesis.
Him: I had like, seven tabs of MLP episodes open for reference material earlier. Just going to check on that horn thing.
me: Talking to a brony on Facebook, and he made an interesting point: "The crystal empire city is a six-pointed star, and it acts as a magic circle that amplifies emotional energy and projects it over Equestria." To which I said, "Oooh! Civic-scale occultism!" *
me: He also said "This also is reflected in Twilight's cutie mark, a six-pointed star. It's like their version of a pentacle."
Him: I had an idea like that, the Crystal Empire was one of probably five or six locations all over Equestria of special magical significance. Probably six places, one per element, although if the Crystal Empire is specific to Love then the other locations are either also powered by love or other aspects of friendship not covered by the Elements.
me: *ahem* "LOVING kindness, it's an easy feat"
Him: Yes, Sombra's horn is specifcally shown as being intact. Hahaha XD Unless there are two stained glass windows of the Mane 6 defeating Nightmare Moon, they replaced the window of the element bearers with a window of Spike delivering the crystal heart.
Him: Waaaaait a second. What was the book that Luna summoned? I didn't see that last time. Tt had stars on it.
me: We don't know yet. But yes, very mysterious. With lots of meaningful looks between the sisters regarding it.
Him: It's probably something to do with what Luna and Cel were talking about before Twi showed up.
me: Yes. And also why Cel was giving Twi more duties, and room to fail.
It's a book containing prophecies set down by Starswirl the Bearded...
me: Could be!
Him: Starswirl is referenced in four episodes off the top of my head. Maybe it's only three. Luna Eclipsed, Hearth's warming eve, and It's About Time.
me: Still, it seems plausible.
* This would further explain why Celestia didn't want the Crystal Empire to fall; it was a matter of national security to Equestria. And having the Captain of the Royal Guard marry the heir to the Crystal Empire is not only a smart political move, but also provides Celestia with constant intelligence about a potentially magical WMD.**
** From that same Facebook conversation I was having:
Other Him: So Princess Celestia is also that magnificent bastard Xanatos as well as being Sol Invictus?
me: That's my contention. Also, she has an incredible spy network, because: We have seen Pegasi Royal Guards, and we have seen Unicorn Royal Guards, but have we seen Earth Pony Royal Guards? (Okay, probably, but work with me here.)
Other Him: Yes, an army of spies. Just nomal looking folk. That's what the patrician of Ankh Morpok does, in Discworld. Just hires schmucks and gathers intel, then has professional spies sift through it. Also this is sorta supported in the show, what with Pinkie using stealth a lot. PINKIE SPY
me: "The name's Pie. Pinkie Pie."
Other Him: It would explain her employment at Sugar Cube Corner, despite her never really doing any work.
If you're running a pony campaign and all these ideas do not set your mind to drooling with the possibilities, there is something wrong with you.