Great summary of the current VR offerings.
I have access to a Cardboard, gear vr and a vive. I would like to make something for vive eventually. I have a few ideas for more complicated games on these platforms but I I’ll focus on something smaller for my first project. It’s a silly goal but I believe it’s a great small achievable project once I’ve learned my way around the IDE.
I’m a professional trombone player but quite out of practice at the moment. I worked on cruise ships and played in lots of wedding bands. I recorded an experiment in AltSpace VR a few months back where I held my controllers and played trombone for the random occupants. https://www.youtube.com/watch?v=vBUjEqWUy8I
I realized that with limited digits the commonly learned musical instruments such as piano and guitar were hard to navigate in vr. Instruments such as the Trombone, Cello and theremin would be much easier to translate in the virtual world as they usually require one location from each hand.
The trombone presents less hurdles than the piano. The only variable I haven’t figured out is how to determine air speed. This is required to determine the pitch/velocity of the note. I’d love to experiment with the vive’s onboard microphone but I’ll probably raise and lower my left hand like a theremin.
Perhaps with the upcoming vive knuckles piano will be easier to play. I imagine in 5 years we’ll all look back and laugh at these limitations.
So uh… there’s my goal. Grant me knowledge my internet friends. 
Dean