I feel like I'm one of the only people who thinks that it makes sense, and
isn't "THE. WORST. POSSIBLE. THING!" I mean, the show has been building up to this for awhile, hasn't it? She's the student of the princess, gifted with magic, and a consistent savior of the world. If you ask me, it seems pretty obvious - what, with all the lessons - that Celestia has been grooming her for this for years with tests of both skill and compassion. Heck, her element is even a freaking crown.
While I don't know how accurate
this source is, it sounds like they don't plan to change her personality or relationship with the cast much, easier. The "new challenges" makes it sound like she'll become sort of a princess in training. Basically, the only difference seems like it's gonna be her ability to fly. (Again, though, I don't know how accurate that source is.) Celestia's special talent is moving the sun, while Twilight's is ALL magic, period. Quite frankly, especially with the "never seen a unicorn with your raw ability" thing when she first got her Cutie Mark, it sounds to me like her power may even be capable of surpassing Celestia in the distant future, if she hones it properly.
Basically, I support the decision to make Twilight an alicorn, if it is in fact made. I don't think it's even close to jumping the shark, as some people seem to be convinced, and I don't understand how some people are saying this one thing might ruin the show. As far as I'm concerned, make way for the honorable Princess Twilight Sparkle, if she is in fact coming at all.