Yeah it was a bit forced, but there's always been conflicts between the Night Elves and the High Elves. Just look at the Highborne in Darnassus and what Maiev did to them. But still to this day there are High Elves, who are part of the Alliance. You see it with the Silver Covenant, you see them in all kinds of places, but it's never really a big theme. Maybe when the next expansion really is about the Legion and there's Turalyon and Alleria and their son Arator we might see some High Elves as an Alliance race. Then again it would be interesting to see Alleria come back as a Blood Elf, because of her exposure to fel magic.