Support for VST's and a integrated DAW playback software.
I think it would be nice. I am saving up for EASTWEST QUANTUM LEAP SYMPHONIC ORCHESTRA (caps weren't mine) and REAPER 5 at the moment because musescore does not support DAWS that much. This will mean I'm using three different softwares to create my music. Perhaps this is something to be implemented in musescore 3?
I know Sibelius is going down this road, and while I know I'm never switching it would certainly give you the edge. for the program, since it would be free.