It's post like this that makes me proud of this community.
Anyway, I too thought of the problem like Graf Zahl did and I'm afraid a language will not be enough.
You'd need an OS that actually acts as the intermediate to assembly code translater of today's compilers. All apps on this OS would have to be written in a very high-level language with a degree of abstraction much more important than what we have today (don't ask me in which form, I have no clue, but probably exhibiting properties similar to Haskel) and an equally high-level standard library.
The idea is that the more high-level your program concerns are, the more opportunities for optimizations there is (somehow counter-intuitive but I think we, coders, tend to confuse having control and writing efficient code).
Oh well, anyway, just wanted to contribute to this fine discussion :)