I think it would help a lot if it were the norm for DEs to come with a bunch of prefab configurations right out of the box, which the community could then add to. It'd be cool if configs could be exported and shared too.

That would give many distros much less of a reason to exist, and could instead be configuration profiles for GNOME, KDE, etc that could easily be loaded on -any- distro. It would also allow the configurations to be iterated on independent of distros which would eventually lead to much higher levels of polish.