I dunno. Probably some kind of firmware interface standard. Hopefully it'll be extensible so the same base design can adapt to a large range of hardware profiles and features. It sure would be nice if it was a unified concept as well so there could be wide ranges of compatibility.

Only kind of kidding. I imagine the future for a while will either be continued growth into proprietary firmware platforms (like Apple and how tons of other phones/tablets have done) or a reworking/adapting of the main concepts behind UEFI but maybe making it less like ancient Microsoft-like patterns. Potentially something like u-boot becoming more common, or things like LK (Little Kernel). I think we'll see more evolution instead of hard replacement of concepts.