Non-destructive midi quantization (a la Logic), including quantize strength. Better midi over dubbing (automatic clip merge as an option).
A way to easily map a sample to a trigger note/step sequencer (a la FruityLoops or Live's Simpler), drag and drop from an audio track or the browser would be great. I do have Battery and obviously there's Session Drummer but it makes for a somewhat cumbersome workflow compared to those other examples.
An easier way to access external samples in Drum Replacer.
AudioSnap placing transient markers at the correct spot at least 95 percent of the time.