I am vehemently apathetic. I don't think it matters whether or not she is an Alicorn, sure she can fly and increase her magical aptitude but it makes no difference as long as the writers keep up the same degree of character development and conflict. My friends concern was that they would make Twilight way to wiser, like to a degree of the intelligence of the other princesses, but I feel as though that comes with age, not race. I personally feel that it would work because now twilly can screw up even bigger and, hey, maybe even give us a three parter, who knows? But she could also grow awkwardly tall and get way to OP so, yea there is that.
Overall I can say with passion that I don't care