So I'm imagining a pacific-island-navigate-by-the-stars simulator, maybe speed up time so 8 hours of night become 30 minutes of cardio. Choose a couple of islands to row between, get some directions of which star to follow, and get to work.
Good news: some water simulation and a night sky are probably just a library include away, right?
Bad news: would have to do something fancy to nail the motion sync, I was thinking an arduino and some hall effects, really just need to capture the bookends of each rep and adjust the video to match your movement. I guess goggles already do position tracking but I think I would basically want to predict the snap when you change directions, as even a few ms lag will ruin the immersion.
Alas, I am merely a web developer without so much as a pair of goggles, but I think this will be a good starter project on account of not needing to create any assets. Godot looks very promising. If anyone else has VR-but-good-for-your-body ideas I'd love to hear them.