In what ways does Session Drummer not do this presently? This isn't a challenge I actually want to make the list.
Despite the view, SD is essentially "pad" based. But AFAIK it won't do the following:
Layering - I seem to recall you can edit the underlying kit file with a text editor to get layering functionality? But still, can't do it in the UI
Swapping samples in/out on the fly - AFAIK you need to stop transport to do this?
Erasing "bad" hits - okay that sounds pretty cool
I always use SD with a keyboard but can you not assign the notes to pads on a controller?