One thing that I'd love to see is a system for adaptive edit/delete windows. Right now it seems to be a fixed length of time (I want to say an hour?), but I think it'd be conducive to better conversation to have flexible windows, where -- and maybe this isn't the right approach -- the window is extended by X minutes for every reply, or something along those lines.

It'd certainly flatten threads a bit, especially in the case of someone posting a factually incorrect comment and correcting it after the fact.