I don't think it's so easy to assume which way Alleria is going to turn. One one side there's high elves stillloyal to the Alliance, commanded by her sister. On the other hand, her homeland -what she did all for, really- is now under the horde. I personally believe she would go Alliance, but expect a lot of angst and possible desires to reunificate, or simply retake Quel'thalas.
That's why an expansion with high elves would be so interesting IMO.