> Which begs the question why the hell they didn't work on getting the apps used for browsing Reddit to display ads? Just include them as posts like they do on the website, perhaps just with a label added. If the apps try to filter away the ads, revoke their API keys.

Yep, that's what Telegram did - there can be ads in public channels, they're clearly labeled as such in the API, and third-party clients must not filter them or will get their access revoked.