...The Legion has been a big part of WoW since Warcraft III. Old Gods so(Back as TFT anyways). There's nothing bad in either theme. Political intrigue can only go so far. Besides MoP had the faction vs faction thing and well I don't think we need that for a long while.
OT: If Kul'tiras doesn't appear in Legion(same with Zandalar Isle) then there's a bit more land to explore. There's also the fact the Naga haven't had a big involvement since Vash'ir as well.