- Mandate as part of the TOS[0] that API users must display the ads in the application unless they pay a higher fee. I get alot of people use 3rd party apps to escape ads, but this wouldn't be the end of the world, it also allows the developer some discretion on how the ads can be formatted visually which could actually be a big win for Reddit in some ways. Make all this contingent on app review and auditing of the app.
- Work with the community to establish a more reasonable API fee. I'm sure everyone can find an agreement here somehow. All but the smallest players likely would find this agreeable.
- Only allow premium (and therefore ad free users) to use 3rd party apps. If they aren't a premium Reddit user they need to use the official client. This seems like the most pragmatic option to me, since those users would by pass ad revenue anyway.
[0]: Terms Of Service