Musikame has just unveiled an experimental web-based project that lets you 'DJ' SoundCloud tracks from within your web browser.
This is far from the finished article - indeed, SoundCloud DJ player is currently in beta - but it provides an interesting glimpse at the kind of mixing functionality we might see in the future.
Tracks can be selected and cued up via a central browser, with the waveform being displayed above. Crossfading between tracks is done automatically, though a slider does enable you to select how long (in seconds) this will take.
Other features currently include a looper, a pitch slider and an FX pad.
Everything looks and feels rudimentary at present, but this definitely feels like a project worth pursuing. Assuming you've got Flash installed, you can try the SoundCloud DJ player here.