It would be nice if we had the ability to restrict individual users from editing posts instead of having to come up with a group permission mask and put them in that.

I could see this as a feature in the warn panel, along with the other stuff like 'add to moderation queue' or 'remove posting ability' that you're presented with when increasing a user's warn level.

Something like:
"Remove user's post editing ability?"

And you'd be able to specify a time frame or select indefinitely.