Cancel a tag lookup
Tag lookup configurable to optionally ignore anything in () or [] {} in tag lookups
Ability not to save artwork to tag, or to tag & file or just file or not at all. 
The only big things I can think about are:
Rhythmbox and mpd library support.
Library stuff, like finding duplicates, maybe some stats (I hate that
most programs don't provide good lib stats)
The filesystem browser needs some updating. It needs to update the
directory tree if it's changed. And keyboard-surfing should work too.
A better console version. It shouldn't do much besides editing tags,
running functions/actions.
Integrating the logging thing with the whole app and having logs for
most everything.
Massive, massive code cleanup.
Docs for everything that needs it like plugins and all the new stuff.
Drag and drop album art (this seems like it'll be a cinch to implement).
Alternating colours by album instead of row.