Yeah I totally forgot to address that point. My stance is this:
I just simply don't see osu becoming an mp3 sharing site as a possibility. If it would happen as of the result of this, it definitely would have happened long ago. It would be an enormous hassle to try to run a piracy ring around uploading 1 song at a time, and it'd be quite obvious if someone were to upload an entire album in a single upload. No one is going to put in the time and effort to upload raw music here when they could easily do it on any other site, y'know, like ones made for that sort of thing. This isn't an issue with other rhythm games that have custom maps (be it community ran or not). Why would it happen on osu?
Another way that I know this won't happen is that you can upload 320kbs mp3s already. It's not rankable, but if you're using osu to pirate music I don't think you care about ranking your uploads of pure music and likely no map.
Just for the hypothetical, let's say people DO start to use osu as a service to upload 320kbs mp3s to. There's good moderation here. Maps are removed all the time for violating the song content rules. Remember that time monstrata uploaded an Attack On Titan episode in full and it got removed within a couple hours? The staff and volunteers wouldn't allow such a scenario to ever happen.
Edit: Something else I may add, if an artist wishes not to have their song uploaded, they can file a DMCA. It's always worked before. I don't think artists are seeing their song on osu, but are FIRST downloading the map and checking the audio.mp3 file and running it through spek to see if it's 192kbs or 320kbs. osu has systems in place for copyright and they will continue to work regardless if it's 320 or not.