I can imagine Soundcloud adding advertising in a way that doesn’t betray its soul.
The company’s soul is to serve sound creators. It’s not to serve advertisers. Thus browsing the site has no ads.
However some sound creators, basically the highly visible professional acts, need to monetize their plays. They don’t mind paying for hosting and a widget but that’s only part of what they need. Soundcloud is underserving them without enabling ad monetization. It serves their needs by enabling them to earn money from ads.
Problem: how can it sell advertising without gettings its incentives misaligned? It must continue to serve the bands first, not the advertisers.
Solution: If Soundcloud didn’t take any cut of the ad revenues, its incentives would remain aligned with the sound creators. It could charge a flat fee for this option, and create APIs that enabled third parties to sell ads.