1. The ability to mix and match drum kits. Instead of locking us into the 16 sounds, let us create our own kits by drawing from all the drum sounds. This would go a long ways in providing variety.
2. Let us shrink the track height. Once you have a bunch of tracks recorded you don't really need to see things like notes and audio, or even the record and freeze buttons. Letting us shrink down the track height would make it a little more managable, as opposed to having to scroll through all your tracks.
These may already be in the works, if not I hope you at least consider them.
In addition to being able to mix and match drum kits, it would be great to be able to create new ones from scratch too, based on audio samples. Another drum related request would be to have the option of exporting the drum track to individual audio files.