Pokemon Mystery Dungeon - but much more in the style of the first two than the last two. EoS is the best game ever made, GtI was dreadful. Super was a massive letdown, the story was super poor and dragged way too hard; gameplay was much worse in Super as well, nowhere near as engaging.
Conquest, or alternatively a FE crossover SRPG game. - Conquest was the last great spinoff. A sequel should have come for 3DS, it was such a great game. I would love one now.
HD Colosseum/XD ports, or an entirely new Orre game - Colo/XD were both fantastic games that had incredible charm, and felt fresher than any Pokemon games that have come since (they still do, surprisingly.)
Pinball and Snap would be great too.