Cover songs are fine, they are not being offered for sale - if they were you would need to go through licensing etc. You can play cover songs in a pub because they have a blanket licence - but you have forever been able to post transformative works anywhere - regardless of legality, don't have to think twice about posting a cover on youtube, soundcloud or any other website for competitions (imagine open mic if it was illegal to perform other people's music lol) if you performed it. Using samples from the original song or the original song itself without permission is where the trouble occurs and that needs to be policed seriously. I mean, what's stopping someone from re-uploading anyone's music? Nothing and that will be a problem one day imo.