Warning: Spoilers to season 4 and beyond, plus speculative spoilers and lighthearted banter
Since the very early episodes of the series, Starswirl the Bearded has been referenced again and again, but never in the flesh. It's hinted that he's no longer around, but we're never told why. We don't even know who would know about what happened to Starswirl really; does Celestia keep that information a secret? Is it public knowledge? Is it a mystery to everypony? Well, my theory is...
The call is coming from inside the house! And by that I mean, Starswirl is inside the Cutie Map. Insane? Possibly, but let me write out my reasoning.
Starswirl may have little known to the show's viewers right now (Excluding information to come from books, comics, etc. It's not that I believe they aren't relevant, but I do think any number of continuity errors may have happened accidentally over the years), but we do know that Starswirl was around the first time Tirek came around to Equestria. We know he put away the sirens, made the time travel spell, and was acquainted with Celestia. While taking a small leap in assumptions, I'm going to say Starswirl might have been around when the Tree of Harmony still had the Elements of Harmony originally; don't worry, later information will help tie that assumption together better. But what does that matter?
"The Elements are connected to the tree, the tree is connected to the chest, and the chest is connected to all of us... There must be a connection!"
Yes, Twilight. You've already pointed out multiple connections before you declared there has to be one. You're supposed to be the smart one!!
Anyways, All of these things spawned from the Tree of Harmony. But why? And what spawned the tree in the first place? Well, that's where I believe Starswirl comes in. While we don't know how long ago Tirek was imprisoned, we do know that he knew Discord. While they could have met beforehand, it still could tie Starswirl to sometime 1000 years ago, when Celestia first removed the Elements to defeat Discord, probably a few other villains, and then Nightmare Moon. I think the tree could be tied to Starswirl; maybe as something which sprouted from his grave (Dark, yet I don't believe out of the question) or he got tied to it by some magical means.
The tree always seems to help Twilight and her friends: it gave them the power to defeat Tirek, a new home immediately after theirs was lost, and it now points the mane 6, Spike, Starlight, and potentially others in the direction of problems to be solved. But why would a plant know or care about all of this, and why specifically Twilight's friends? And why does it require them to learn things about themselves, and go through hardships to open that chest? Whether it's Starswirl or not, it's definitely sentient. It's teaching and guiding, which is what some theorize Starswirl did for Celestia.
But the strongest evidence I have to link Starswirl with the map was a very specific piece of animation, that I originally didn't notice.
Starswirl's spell; the same one Starlight realized she could tie to the map, was taken away by the map. Why? They didn't touch it again, and why the attention to connecting the scroll to the map with that beam? If the spell was going away anyways, it wouldn't have that beam right? I think the map purposely took it away after the job was done, knowing Twilight would succeed and that sending them all to Starlight's village in the first place would eventually cause this to happen. The map has always been more knowledgeable on the goings on in Equestria than even Celestia, and while it originally seemed specifically linked to the mane 6 (With their elements, cutie marks, throne-mark-beam things and such), now we know it isn't limited to contacting just them.
What do you think? Is Starswirl helping to keep the peace and guide Celestia's student? Or is this all still insane and I spent way too much time thinking about nothing?