actually, for me, what I'd want in a MusicBrainz app on my android is the ability to actually * tag* musicfiles.
Why? well because loading a bunch of files on the phone/downloading them from wherever (I'm sure bandcamp and soundcloud m.m has apps with features) and then only later discovering that it was badly tagged (and therefore messed up playing order etc.) and being able to fix that on the get-go instead of having to plug into a computer (that must have picard on it, so not just a random public one or anything. also to remember an USB cable.)
Or the situation where the way it's tagged for musicplayer on computer, works havoc on phone.
For example does itunes let you set disc numbers and will play these separate and consequently, not so on a phone or mp3player - instead you get track 1 from disc 1 and then track 1 from disc 2 etc.
perhaps a "Mobile Picard" is a different project altogether ?