I'd like to support the idea of improvements to the Theater View core - esp wrt to plugins and skinning. There are some really nice front-ends out there, and I still feel that this is one potentially major area that MC can improve on to keep up.
Admittedly, the DLNA improvements could potentially make this less important, but then MC could be seen to being relegated somewhat to a server-side role.
Another thing I'd like to see is improved multi-library capabilites. Preferably, the ability to have more than one library viewable at a time - allowing a 'master' library and personal/transient libraries.
C.