See that's the problem with all those social type of sites; you never know what they'll change. It's perfectly fine to want to monetize your site, but it's best to do it early on, rather than later when you have a solid following and you'll just piss them off.
If anything, SoundCloud should keep it like it is and add a VIP type of pricing, if you want to. Ads should be at a minimum. With all the users they have, they don't need to plaster the site with tons of stuff.