Many are admittedly hard challenges, but;

  > Give me a non-browser client.
  > Make the browser client not leak memory.
  > Don't interleave Soundcloud Go previews with free music.
  > Give me reasonable discovery of similar music.

Until Go happened, Soundcloud was my everyday work listening. Now I only use it for long mixes that I can't find (or am too lazy to find) elsewhere.

The challenge for any clone isn't going to be features, it's going to be content.