2D Games, apps, and ware!
But in all seriousness, if Nintendo did all these things I don't know what I'd do :
* WiiU Connectivity
* GBA VC (More than just Ambassador games)
* Somehow import saves from original NES/GB/GBC/GBA Games/carts to 3DS VC using official Nintendo means (This is more like an unrealistic dream though)
* 3D Video chat
* Flash (Probably Flash Lite if at all) in browser, or a better integration with HTML5
* Virtual Boy VC
* A licensed app to create 3DS channels (similar to the app that was on the JP DSi, channel creation was limited but still)
* GameCube ports (Would love to play GC on a handheld)