The biggest opportunity I see for ads on Farcaster right now:

1. At the end of a frame flow, when the frame has nothing left for the user to do, enable the frame dev to serve a *personalized* (and paid) recommendation in the frame
2. Enable frames devs to monetize their frames by adding an ad frame in the frame flow

Building Larry, FOSS via @frames, @framesfun /open-frames to help decentralized social win. a16z CSX23. farcasterchannels.com farcaster.id

What prevents someone from creating this already?

I'm eth newbie..just learning
(working on @farcaster)

terminally.online

nothing - hence the suggestion of the opportunity :)

been there, done that 😉 
try it:
https://ad606.c13studio.mx/api