It would be great to be able to have an increased number (or unlimited?) number of MIDI parameters that can be controlled by an external controller. There is currently 8 in MIDI controllers/New Mapping/Change Param 1-8 but a lot more would be really useful.

Support for relative encoders would also be amazing (so CC number 0 turns the knob left and 127 turns right) so you don't get jumps when you change between different instruments.