Sounds elitist. This can already be done. If someone appreciates your post, they can zap, period. If you post something and someone disagrees and wants to comment, then they have to pay?? No one is that special. Nostr about free speech, and this is anti free speech. Again, no one is that special.
Discussion
It’s not anti free speech
Ahem:

It’s not like anyone would be forced to use it.
Pro paid speech*
Why dont you just come out and say that you are choosing to spend your time posting on nostr, and want to earn some sats from doing so, maybe make a little side hustle from it. Then i could understand that, and i get it. But to say that this would help nostr to stop bots or spam sounds disingenuous. Just say you want to earn some sats from it, and be done.
You really don’t understand what I’m talking about or my motivations. Which is ok. But to clarify I don’t earn anything from being on nostr. Nor do I really care to. People zap me and I zap the sats right back out. It’s a circular economy of zap washing. What I’m interested in is figuring out how to add weight to speech and make it costly for bad actors to abuse the system.
Proof of Sats
Im not sure we can have "good quality speech (Signal)" without some degree of "bad quality speech (noise)". Arguably one man's trash is another man's treasure too.
One challenge is it may well become like x / twitters "freedom of speech, not reach" policy if it went the financial route.
Which I'm not sure if this is the best overall outcome for all either, even if there are benefits.
Would a better strategy be to allow functionality for folk to amplify and attenuate signal / noise in some way i.e. via
Communities / Groups?
Those good at picking up Signal might help others find it also. Perhaps with a small entry fee or credibility qualification into a Community.
Sorry - I feel like I'm offering more problems than solutions. Something like this probably requires a fair degree of prudence. Though I like what you are driving at in many ways.
Some degree of bad actors has to be allowed I think for it to flourish. The OG Bitcoiners / Cypherpunks were arguably 'bad actors' once upon a time.
Is elite bad?