Some years ago I came up with a challenge that I felt was possible with the right support: a JRPG-style adventure RPG that was 100% playable by blind players, using nuances in the language of music to deliver complicated information. This is something that I can't go anywhere with without help, but if I had one wish, I'd like to see someone get it done in my lifetime. I can't offer more details because exploring it takes access to a programmable synth and knowledge of musical composition, but I feel that the core of the idea is there.
The idea came to me when considering how in some game soundtracks (no points for guessing that Final Fantasy VII is on the list) incorporate character themes into other game themes--places where they live, for example. I wondered if a game's battle system could dynamically generate music by combining character themes on different instruments: the swordsman on guitar, the healer on piano, the wizard on violin, opposed by two goblins, each one a simple drumbeat. The health of each character might correspond to its volume; negative status effects may make the character theme stutter, race, fall off-key, or miss notes.
In sharp contrast to a lot of my projects, such a game would need to be heavily produced and directed. The story, whether linear or branching, would have definite and defined points in the story that have to be figured out ahead of time so that the music can be carefully woven. It would also take a lot of talent: musical, voice acting, writing, and direction. Anything less than great talent would make a mediocre game, and while it might serve as a proof of concept, I dream of every project knowing that it CAN be a great work of art--but it may never be.
And make no mistake, I am guessing that the complicated use of musical language can be made to work. I have a strong hunch, but until I can get good talent to help try it out, I'll never know for sure.