I'd love to see all races share the spotlight and not just a select few, especially humans and orcs. Forsaken I feel had some in Wrath and some love in Lordaeron leveling in Cata. Thinking trolls will have some more in MoP and Blood Elves are having their share of awesome. I do feel Tauren and Goblins don't really have any big moments in lore, they're just there, Goblins moreso just being there than Tauren, at least the Tauren leader is around!
Night Elves had some love with Hyjal in Cata and are around a bit in MoP so I don't see them in any big need of lore. However, the rest of the Alliance could use some... I don't see the dwarves, gnomes, draenei or worgen doing much of anything major. I can imagine the Draenei will have a big role in a Legion expansion, but dunno with the rest...
So who should have the next bit of lore? Dunno, but I think I'd go with an Alliance race, feels like the Alliance is mostly just human activity right now.