I like the idea of in-memory change detection... there's a definite use there. I don't agree with the idea of storing all files in memory (especially given their complaint that Git is slow on 20GB of files...), though I admit grepping that is fast.

But what if it were simplified to just a live ls-diff based on when a command was last run / a timestamp? If Git / Make would hook into something like that it'd be really useful.