Relatively simple actually, without copyright. Download Spotify, rename app to Spudify, re-upload to app store. Done, easy peasy. Hardest part about it would be decompiling the existing app, which is definitely possible and may not even be necessary.
The real truth is, however, that in this hypothetical world there would be no Spotify to copy and there would be much, much less music available to stream on Spudify.
Yeah cuz musicians and artists only ever do it for the money…no other reason ever, nope.
If they can’t afford to do it, then you’re relegating creativity to only those wealthy enough to be able to afford to do it.
The vast majority of art throughout human history was paid for by somebody, or sold by the artist. Van Gogh dies a poor man because people didn’t want to buy his paintings when he was alive. The Sistine Chapel was commissioned by a Pope. Just because you think your have an intrinsic right to the work of somebody else doesn’t mean you do.