Band Generator - There's something I love about this. I don't think Fandalism can just "generate" a band any more than LinkedIn can "generate" a startup. That said, it seems like musicians are always looking for the equivalent of marriage (a band) when I think it might be more fun to just have a several one-off trysts (random jams). The latter isn't really something musicians do currently. Which is an obstacle. But maybe there's a way to spark this behavior using a "random person to jam with this wednesday" generator.
Worldwide Music Battles - In theory this sounds really fun. I recently did a contest with Interscope records to promote the new Van Halen album. Musicians performed cover versions of the new Van Halen single in exchange for the possibility of fame and fortune. There weren't as many entries as I was hoping for. I think it comes down to musicians as artists -- and artists want to be free to create. They don't want to be told what to play. I think. Or maybe they think contests are cheesy, and your idea is more legit. I'll experiment.
Collaborative Online Recording - I think indabamusic.com does this. At least, that's the impression I get (I haven't used that site yet). It's surprisingly non-trivial to just throw a drumset recording over your bass line. To get a good drum sound you need a few mics, a mixer, recording software, EQ & mixing skills... it's really easier (and more fun, for me at least) to just jam with people in real life. And record it.
Thanks again for these ideas. They got me thinking and I'm sure I'll use them in some regard as I build new features. Same goes with all the awesome comments in my original post.
I'll keep blogging as I add new stuff to Fandalism. I plan to add a lot of stuff that was suggested in HN, in one way or another.