@jcsteh Yeah that was the first thing I thought of with getting lives back, and I think it would work well. I also like the idea of adding different loops at different tempos.
Big thing I'm worried about is just how to curve the difficulty progression of the melodies. I actually experimented with a similar idea a few months back. I tried adding more notes closer together to increase difficulty, but I didn't like it. I don't know if i'll be coming back to that project any time soon, but if I did, I'd likely make a probability system where certain steps of the sequence are much more likely to have a note dropped on them. As just one example, the first note of each beat has a higher chance than the rest. Or something like that, I'm still nowhere near done mulling it over. Anyway that could be a powerful dimension for difficulty adjustment.