Before you all read the title and reply saying it can't be done, know this: I do not know much about code or the minetest engine.
I've been doing a lot of reading on the forums (particularly in feature discussion and general discussion) and have been noticing a lot of feature requests that could only be implemented in the minetest engine (i.e. not with LUA mods). I've been thinking that if there was some sort of C++ add-on api, that a lot of these problems could be solved without much work on the developers' part.
This would solve much of the debate over other dimensions, better mobs, virtual reality support, and gamepad support. Keep in mind I have NO IDEA how any of this could be implemented, but if it is possible (and practical) it could solve a lot of problems.