I honestly see it as a logical step. Twilight is already massively over-powered, belongs to probably the most powerful Unicorn family in Equestria, and has been the only personal student of Celestia that we know of to have been under her tutelage for about ten years. So, realistically, what else could they do?
Yeah, the princess bit is far-fetched. We must remember that, not matter how sizeable we are as a fanbase, we do not influence the main story of the show. Jason Thiessen himself said that they would keep the show the way people fell in love with it and that means still keeping its demographic audience as its main focus. If Hasbro think that the kids will love it, they will go ahead of it, no matter what backlash they would receive. Pleasing everyone is so very hard, it seems.

Besides, it's not as if the other characters have to leave everything they've ever known behind and live with our "beloved Sparkly Alicorn princess". They still have a "life in the show", away from every aspect of Twilight's. It's not as if they're all becoming Alicorns. After all, one very serious aspect of friendship and love and life that the show is yet to deal with is learning to cope and live while your friends are - heartwrenchingly and quite beyond their control - torn away from the life and friends they know.
If the characters are able to overcome this without drastic measures (I'd imagine that there would be a lot more backlash if it was revealed that the others all moved to Canterlot), then they would be given far more opportunities to develop in the show.
Besides, maybe it's time we had a Twilght break?

I may dislike Twilight as a character, but I do see that this can be beneficiary in terms of character development. She's already way overpowered, as I said earlier, so what harm could come from merely officially confirming this high power-level?

This was my first thought when I saw the Crystal Empire episodes. A test for Twilight on how she would handle saving an empire can only really lead to can she lead one too. Not happy, not sad. I just wonder what the others are going to do with her not around anymore...Ponyville will be so boring.

I kinda knew this was gonna happen the second the Alicorn Twilight things started popping up. That kind of stuff is rarely an accident. And hey, just because she's becoming a Princess doesn't mean she has to leave Ponyville. She can do whatever, she's a fuckin Princess. Also, way too much chaos happens in Ponyville to justify having Twilight leave it. Especially if she becomes more powerful. I don't think Ponyville will blow up any less now that Twilight's gonna be a Princess. Unless it was her un-princessness or maybe even her presence that was causing all the chaos. But that would be weird and convoluted and what. Also, her leaving would be a sad ending. This is a children's show, and those usually have happy endings. So, my prediction:

Twilight: Hay guize I has wings now.
Rainbow: HAX
Fluttershy: Oh, good, now I can just go hide in a corner cuz you have 2 other pegasi now.
Twilight: Where da fuk u goin
Rarity: Twi's right, u get bak here u bish. We not done wif u.
Pinkie: NOOO DUN LEAVE QQ
Applejack: Wat u want me to say. Wat.
Rainbow: Tell meh you luff meh!
Applejack: Okay. Ilu
Rainbow: Yay
Twilight: U guize r weerd mebbe i should go to Canterlot
Everypony: NOOOOO FUK U I HAET U
Twilight: Okay gawsh I stay
Pinkie: Yay!
Rainbow and Applejack: Too busy to respond if u no what i mean
Twilight: Okay princess I stay
Celestia: Ew, get away from me, u not a lesser race no mores. I dun love u no more
Twilight: Wat! QQ
Celestia: If u reed any fanfiction im obviously a pedophile so now u like me it no fun no more
Twilight: NOOOOO BUT I THOT WE HAD SOMTHING TOGETHYR
Celestia: WELL TOO BAD BISH! TO DA MOON
Twilight: NOOO
Celestia: ...Fuck y i do that.
Pinkie: She comin back?
Celestia: She a fukin princess. If she can't teleport back she a nub. Like Luna
Luna: Hay i was crazy shut up
Celestia: that's no ascuse.
Luna: Fine
Celestia: Kay, that's enough wall of dialogue. or like... polylog cuz there's like, uh, 11teen of us here... kby
POOF
DA END
OR IS IT
NO IT IS

I'd switch Lauren leaving the show with the Cheerilee and Big Mac Hearts and Hooves episode, but you get the idea. This is hardly the first time the show's been "ruined", fandoms be crazy.

As for my thoughts, I ain't even mad.