The problem I think with this would be

- how do you find out exactly who has read your post & how to notifiy you of that ? With reactions maybe? (And those are also approximate -- if someone is reading your post & reacting to it from a relay that you don't read from, you'll not find out)

- bots - how to prevent zapping bots?

The other way round (zap first with a link to post or just a promotional message) has been tried - it's called zapvertising