Yeah and this is smart because this time around the licensing falls on Spotify where as back then TT had to negotiate licensing if I'm not mistaken. I'm not a lawyer but if that's true this seems much more viable using Spotify's APIs with the caveat that your entire business relies on them if that's your aspiration. Regardless, wish I'd thought of this :-P Seems like it would be such a fun app to work on :-) Best of luck to you!
(BTW it just pinned a Google chrome helper on my machine so I had to kill it. Not sure if you know anything about perf. with your app yet. Just FYI)