It would be nice to have a way to play a new track when you don't have access to the internet, as right now the option to play a track you haven't before is simply grayed out when the game is in offline mode.
I found out about this when I was trying to play a new track while passing the time on a roadtrip, but I could only play tracks I had already played before. I'm assuming this is to make sure each song is added to DAT's database, along with who played the track first, and any ghosts for that track. This isn't a big deal now, since DAT is in active development, but it worried me for the future of the game years from now when those servers are no longer maintained, or when they simply go down for maintenance.
Not saying I would like to beat ghosts or stuff like that and then have that data be uploaded when I have internet again, but it would be nice when offline to be able to challenge maybe a locally stored ghost of my own top score, and of course to play songs I haven't yet.
Anyway, really cool game! I've enjoyed what I've seen so far. After you removed the issue of hidden barriers from track generation, this is pretty much the only complaint I have.