Majority of nostr doesn’t even know what sats are. That’s issue no. 1 with this approach. 

Requiring payment of any kind automatically makes it a private square not a public one. 

Whatever the best solution might be, it has to keep conversation free. 

Also, a tiny fee is a very low barrier to a determined spammer. The only reason paid verification works on Twitter is because the barrier to entry for verified payment is higher, and you get banned. On nostr, being banned means nothing.