Another idea for when there’s a suitably sized community is a Cover-Each-Other-Roulette (CEOR), which I ran successfully in a Facebook group a few years back.
The idea is that a group of artists sign up, then are paired off randomly, each recording a cover version of a song by their opposite number. We made this deliberately random – pairings of disparate styles and backgrounds made for some of the most interesting collaborations – and the whole process was discussed and recorded in forum posts. We ended up with some great tracks from this, and at least one pairing went on to release the produced track commercially and work again on future projects.
I’d love to run this again somewhere. Could this be the place?