I want lazy evaluation. I want to be able to do this:
(setq some-variable (lazy (some-function foo bar)))
And then I want the next thing after that to go ahead and be evaluated. I don't want execution to pause and wait for some-function to complete until some computation actually needs the value of some-variable.
I can't tell from just one small example using metasyntax, but that looks more like you want a future. Those would be nice, but I don't see emacs doing those anytime soon. If you don't want to compute something right away, wrap it up in a lambda and bind it to a symbol. Emacs's brand of lisp lets you funcall a symbol through as many layers of indirection as you want. I think you can even get closures from the cl package, even if they're not implemented terribly nicely.
Selective lazy evaluation is more of an occasional syntax convenience for specific problems like streams, but outside of those areas, it's one of the leakiest abstractions you can get -- you end up having to sprinkle laziness declarations all over unrelated code to maintain the laziness you want.
Much as I love emacs, I think you can be reasonably sure that the emacs lisp environment is purely in maintenance mode and will never see significant architectural changes. You want an editor with a pervasively lazy extension language, try Yi.