Ah, yeah, a note that it remains unsolved might help with reader expectations. I didn't find that it affected my experience that much, but I can understand why it would.
If you want something a bit more out of the box than simply playing a game, give animating a spin! Just a simple flipbook-style animation app, there should be plenty out there. No need for pose-to-pose or anything at first, just try abstract, straight-ahead animation. If you find yourself gaining an interest, it's easy enough to pick up knowledge as you need it (if you do want a jumping-off point, I'd recommend Alan Becker's series[1] on the 12 principles of animation).
It's incredibly fun bringing even the simplest of things to life, and really rewarding getting to look back and see how your understanding of motion and weight grow over time.
I'm definitely not the target market for this, but I do want to say that this really scratches an itch for something that should exist, and I really want to compliment you on how fantastic the execution is! Very clean look in both the physical and digital realms, and I really appreciate just how fully featured it is! It really seems like the ideal version of what this product would be. Also love the idea of the bookmark pattern. Out of curiosity, is that customizable too?
+1 for this! Some considerations I thought of: 1. smaller keyboards don't easily have access to upper octaves. 2. User might frequently change the transpose on their keyboard.
Could there be a Create Bookmark Now button in the app as a fallback?
