The 4-track limitation is stupid. Splitting a track into drums, bass, vocals, and melody instruments is definitely useful for a lot of purposes, but it's limiting for real in-depth remixing. Why not make it unlimited?
Clarification: When I say build hardware, I mean design a usable hardware interface for mixing 4 stems. I don't have to guess what audio is on what track. Imagine what a nightmare it would be if every stem had a different number of tracks and you were trying to DJ live with them.