I'd really like:

• The ability to rearrange audio and bank tracks in the mix and song views
• Subgroups, or the ability to bus channels to an aux track for group processing (yes you can use pre-fader sends, but that's a janky work-around)
• Individual insert effects for drum bank pads
• Fade tabs on the edges of audio clips in the song view. (The option to add cross-fades would be great too for rendered loops that have reverb tails, etc.)

Perhaps BM3 was never intended to be more than a sketchpad for musical ideas, but I really think that with these features you'd have a true all in one solution for mobile music production.