That depends. Both factions saw next to no action in WoD but we still ventured alongside rough counterparts of the Horde and Alliance to make up for it which might be the template used. Legion being Alliance-heavy does not necessarily means the Shadowlands will be, considering how much the place would matter to, at least, both Troll races and Forsaken for starters.
This is all theory of course. For all we know the next xpack is Sylvanas vs The World and Baine takes center stage as The World's last line of defense or some something. Not like we shouldn't expect the dumbest shit to happen at this point.