I want an editing environment which operates on the AST of my code (obviously it would have to support every language I wanted explicitly to do this), so that files become entirely irrelevant, I never have to worry about formatting differences or where things are or whether that function is in that file or that file. A bit like working in a Smalltalk image.

If that was then extended into the version control system that'd be even better. Oh yes.

But getting a new language into these things would probably be a nightmare.