With curated relays. 

A relay owner could potentially manually curate which npubs gets to write to that relay. That means if you only use that relay you would see a very curated timeline of manually picked people that are not bots or AI. 

Of course it might not be feasible to do it, but it can be done already. 

 It seems that what you describe is a whitelist relay which may have interesting properties but probably not a good fit to act as a regular relay free of AIs. 

 I'm not solving captchas for a token lol that idea is older than Bitcoin it's called fatigue operator and bot operators took turns solving each other's capatchas so their bot could run when they were away. 

I like the model where relays handle the bans and anyone can easily spin up a relay.