Yes, given enough (some) time. I'm not the best at python user interfaces though so that would be a learning curve (time).

A simple first version UI would just let you maintain apps list and xref lists but would probably require glade.

The uglier question is what to do about defaults.list and sinking (back) to hildon/dbus apps. Sinking to dbus is still a little ugly like if you wanted to pick between mplayer and Media Player... i'm working through that quirkiness in emelfm2 associations to hildon apps but its still very much a hack with shim scripts and dbus messages that i would want to burn some grey matter and testing time on.