Perhaps a better solution is to give different levels of correctness. Especially for drums and bass. If I hit the note slightly off then it still sounds, but over time I’ll be subtly throwing everyone else off because their note charts aren’t adjusting. If I’m too far off though, the usual happens, the note is flubbed, and it doesn’t play.

This should work. I mean, who plays Rock Band/Guitar Hero based on sight reading alone? When you play bass you listen to the drums to get the rhythm and match that to your own internal rhythm to keep the groove going and lock-in together. When you’re playing guitar you need to listen to your rhythm section, feel the on and off beats with the bass drum, get the eighths from the hi-hat. Feel the momentum and drive of the bass to define the rhythmic feel of the song. If you allow a certain level of incorrectness to be shown by the players as opposed to just keeping their part playing as long as they make it close enough I think it’ll help to replicate this as closely as you can until it starts to move too far away from the core concept. Still… if you want to offer something else allowing it, say, some sort of jam mode (change out different instruments for different sounds… no real way to simulate, say, fretting A on the E string for a fatter sound instead of playing it open) or something… that could be interesting.

2. in doubles mode, you take turns setting the beat, like every 8 bars it switches.

3. say you’re allowed to add steps that aren’t in the chart, and 8 bars later your steps appear in the other player’s chart. and vice versa.