You could even TimeMachine-without-additional-drives... I mean, why should my snapshot system and my backup system be one? How about letting me use TimeMachine locally, and if I plug up an additional drive, TimeMachine asks me if I want to backup to it as well?
Not a game-changer exactly, but a nice-ish upgrade potentially.
The biggest upgrade would honestly just be quicker/continuous replication that doesn't drag the rest of your system down.