I wanna see a 3D game engine with the most versatile editor possible.
I want the 3D and graphics to be so amazing it will even be a viable option to non-gamers to use for creating beautiful terrain/cinematics/movies/etc.
I also want the engine to be able to handle 480x480 maps, 1,000,000 units/doodads, etc.\
With this, good mapmakers should be able to develop games of any type.
Example: For RPG, a game like Zelda (but multiplayer! multiplayer zelda... yes!).
Definitely will happen within this decade, given the current trends I'm seeing in game/technology development.
That, and I'm sure many would pay over a grand for such a game/editor (mainly editor).
Yes there are game engines out there already doing this, but they don't let users make their own, host/share their own like wc3/sc2.