Meowcenary

Gaben's Own Aimbot
Contributor
Looks like I'm a bit old on this, but better late than never

Looks like it's canon

"Although rumors and speculations about the event already made their round on various places, the first official information confirming Twilight Sparkle turning into a princess was in an exclusive article on Entertainment Weekly[1] released on January 29th, 2013, containing an interview with the show’s head writer Meghan McCarthy. According to McCarthy, this was a planned event as Twilight Sparkle "was set up from the very beginning to be on an important journey”

Konwyourmme source

Entertainment Weekly article
 

[Interrogator]

Australian Skial God
Contributor
This makes me wonder...
How will the season 3 finale be, and what'll season 4 be like with this change?
they'll probably do something a long the lines of making the situations take away some of her power ex. "Oh no I can't use my powers in this cave because of some B.S."