It's really wild to me that there isn't a big open source project for portable media players. There's Rockbox, but it doesn't seem to be ported to many modern players.

In the radio control hobby there are like 4 major manufacturers of transmitters and they all run the same open source firmware, which gives the community control over the hardware and for the most part makes things run very well.

It would be awesome to see something like that revolutionize the portable audio scene. Someone start a software project and release a good, STM32-based reference design so that the hardware will be reliable and people can implement good features in software that can run on lots of different devices