I'm not knocking you for using those sources btw, that's a decent way to ignore the hard part of a problem to get to a minimum viable product -- plus licensing tracks is soundcloud's problems. Soundcloud is also ripe for disruption because their interface of overlaying comments on the waveform while playing tracks is at best distracting and at worst causes my web browser to crash all the time.

When listening to soundcloud I use this bookmark to turn off comments on the page:

   javascript:(function(){$("a[class='comments-toggle']").click();})();

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Do you have any additional filters on your sources, or are you straight-up playing the streams as-is?

I'd suggest putting in min/max song lengths (to strip out the 2min previews of tracks that sometimes get posted). Although I think your sources are clean enough to handle that. You probably want a 15 min maximum to skip over mixes that sometimes get posted (or better yet, give a playlist for listening to continuous mixes)

If the soundcloud api provides favourites you could use that as an input as well.

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You could pretty much create a simple version of last.fm by using a "similar artists search" and then mutiplexing the individual soundcloud pages for artists.

So you could have a "sounds like Skrillex", "sounds like High Rankin", "sounds like Knife Party" etc where all it does is randomly play tracks from similar artists.