I was thinking about trying this out, but there are some reasons why I don't think it's feasible.

Where are your comments stored?

What happens when you need to run out in the middle of a fire and you don't have time to make your code compile-able? How do you commit "un-compile-able" changes?

I think there are some really compelling reasons to try AST-checkin - all your loops can now be changed to functional, dialect changes like you mention, etc. - but there are some pretty significant downsides as well.