Serebii pointed out that we knew about a lot of Gen. 4 Pokemon before Emerald was released, so I imagine we'll get the same sort of tease coming up.
Volcanion + Magiana movie this summer, a couple of baby Pokemon/evolutions in the fall, and a new game announcement next winter.
But going back to the thing about Gen. 4, back then we saw Bonsly semi-playable in XD and Munchlax had a bit of a role in both XD and Mystery Dungeon. So, do you all think we could see Magiana in something later this year, like Pokken, just to hype us up? They've already done it with Zygarde's forms and Ash-Greninja in Pokemon Picross, so I wouldn't be surprised.