I would love a replay mode, where you could go back and watch the match you played. Given that they have spectate mode which is a few minutes behind it shouldn't be that hard to implement, right? It would need to have a fast forward/rewind feature too.
It would be handy to watch what happened to improve strategy and gameplay, figure out where you went wrong, or just to relive that awesome pentakill :P
Who's with me?
EDIT: Just realised I posted this in God Feedback, probably should be in Other Feedback. Oops.