This topic sometimes looks hot but is not considered a major issue and nobody has a strong opinion if (and how) it can be solved. Please, follow up with suggestions.
Yes, I don't think its a mayor issue. I don't know about gnome or xfce, but so long I've been asked only once to include a port into the kde repo that used to be in contrib.
Make a contrib-gnome, contrib-xfce, contrib-kde repos and submit DE specific contrib ports there, adjust rules. cons: - makes things too complicated;
I think this would be by far the best solution. It would keep everybody happy, and people don't have to subscribe to DE specific contrib ports if they just want their basic DE. I don't see why it has to be more complicated than contrib itself, the rules should be pretty much the same, and whenever someone is given access to contrib he should also be given access to contrib-* (no need to apply to different contrib repos separately). -- Alan