Another bass player here--very glad to see the option!

The PS3/X360 instrument training game "Bandfuse" (which had the misfortune of coming out around the same time as RockSmith and went bankrupt within like a year of release) had a really great circle-of-fifths training mode...but only for guitar. :(

I mean, if you find me a video that shows how it worked, I could eventually build it (for both guitar and bass).

Basses with 5 strings are relatively common, and even basses with 6 strings are available off the shelf.

An option to disable the display of the name of the key would make it a nice game for ear training.

Yeah, its just that I have to pareto-prioritize. The more time I spend on more niche market features, it takes away time from features that 80% of the people want. I'd rather come back around once I have a fully functional product for guitar players and then start serving the custom tunings, the alternate instruments and so on..