I am wonder why so many presume that she is a corrputed Flurry Heart. I mean, sure, it is possible, but I don't see a reason why she should be the shadowy Alicorn. I mean, why could it not be for example Luster Dawn who turned evil with the time after the finaly? I also saw people who presumed that Radiant Hope is the alicorn. Both is also possible, but if it would make sence, I don't know. And Radiant Hope was not even show canon.
Well, I am also not sure how much the g5 comics are really g5 show canon. I mean, that she is the Alicorn is obvious. But I don't understand why she is not fully shown and only as a shadow. This could hint that she is an already known character.
I also rememebr to saw some poeple call an pony Misty, but I am not sure if they presumed it was her or her unicorn assistant.
If I would gave a random name suggest: Midnight Storm