OK - finally. Two tools and the start of Workshop support.
Access them by RIGHT CLICKING on RIFF VR in Steam Library.
MIDI GAMEPLAY TOOL -
Now you can make your own Drums and Guitar Gameplay tracks for your own music. You can also add the Guitar Notes for your music. This will go easier if you have some music chops!
The Gameplay tool lets you submit to Workshop and share your music, or play locally.

Tutorials:
MIDI Tool - https://youtu.be/TF_4IkiZKe4
Making Drum tracks in MIDI - https://youtu.be/pKdgoefsAKk
Making Guitar tracks and sounds in MIDI - https://youtu.be/pKdgoefsAKk
AND
OBJECT EXPORTER TOOL -
Put your own 3D objects in the Creative Hub Objects Menu to use in game,
Use STEAM WORKSHOP to share items you have the rights to.
Or PLAY LOCALLY with music you don't want to share with the world right now.
Remember - [email protected]