First, a successful implementation of the automation lanes.
 
Second, a multi-tool that works better and more easily.
 
Third, make it easier to select and edit the velocities of notes, either individually or by group selection. (Currently the velocity pane in PRV is literally a pain!)
 
I am on board with those who wish notation would be upgraded to something closer to what Cubase does, I also would like VST3 support, but I don't think either of these will be addressed period in any foreseeable time frame.