Here's something I've always wanted: A consumer music file format that preserves all of the underlying tracks ('stems') so that they can be adjusted while you listen to the song. Imagine listening to a recording and going "ooh, that bassline", and then turning up the bassist and turning down everything else to hear it better. Or easily "remixing" while you listen by eg. applying a filter to only the drums. You could…
I don't know how many people would actually be interested in that, though. It would be targeting a segment of music listeners that are extremely engaged with their music. I don't know if that market is really big enough to overcome the growing preference for streaming services.