I'm pretty sure nearly all wallet apps (except maybe Hive) could use a facelift. The problem is right now I guess most users aren't using Bitcoin-Qt anymore. So the question is where should the new UI work be done?
IMO, as you said, Multibit would probably be a better candidate than Bitcoin-Qt, unless Bitcoin-Qt suddenly starts implementing some stuff that would make it working for the average user on the long run while still contributing to the network. I guess that all that is required is a developer somewhere to dedicate enough time on this to prepare patches and work on them until they are reviewed and accepted (assuming Jim also wants this).
I didn't post this on the Foundation's forum, I guess this isn't the best place to expect a developer will see it and start working on it.