Having posts made by the community itself seems clunky... On the other hand, I think it would be ethically dubious to allow people to edit posts by others and have the author's name remain unchanged.... and equally bad to change the author's name after a minor edit...

I guess the "right way" to do this would be to allow posts on communities to have multiple authors. But while I haven't checked, I imagine that would be a Really Big Deal in a messing-with-fundemental-data-structures way. So if we want to do this (which I agree would be useful) it's a matter of deciding which type of bodge is preferred ;-)