I generally prefer using FLM over Zenbeats for most things. But I have to keep going back to Zenbeats because I love working with polyrhythms and time signature changes. ZB lets me set each track to a different time signature, and change time signatures between patterns on the same track. So that's my big request.
Other stuff I'd find very useful:
- An accent track on the drum sequencer. (a very common feature of drum machines)
- Search, favourites, tagging in sample and instrument selection menus.
- Limiting the piano roll to notes of a chosen scale, matching the "scale" setting of the playable keyboard. i.e. not just graying out non-scale notes.