Perhaps a way to serve ads through the agents would be good enough. I'd prefer that to be some open protocol than controlled by a company.
The problem isn't just that ads can't be served. It's that every technical measure to attempt to block their service produces new ways of misleading website owners and the services they use. Perplexity refuses any attempt at abuse detection and prevention from their servers.
None of this would've been necessary if companies like Perplexity would've just acted like a responsible web service and told their customers "sorry, this website doesn't allow Perplexity to act on your behalf".
The open protocol you want already exists: it's the user agent. A responsible bot will set the correct user agent, maybe follow the instructions in robots.txt, and leave it at that. Companies like Perplexity (and many (AI) scrapers) don't want to participate in such a protocol. They will seek out and abuse any loopholes in any well-intended protocol anyone can come up with.
I don't think anyone wants Cloudflare to have even more influence on the internet, but it's thanks to the growth of inconsiderate AI companies like Perplexity that these measure are necessary. The protocol Cloudflare proposes is open (it's just a signature), the problem people have with it is that they have to ask Cloudflare nicely to permit website owners to track and prevent abuse from bots. For any Azure-gated websites, your bot would need to ask permission there as well, as with Akamai-gated websites, and maybe even individual websites.
A new protocol is a technical solution. Technical solutions work for technical problems. The problem Cloudflare is trying to solve isn't a technical problem; it's a social problem.
I’m not here to propose a solution. I’m here as an end-user saying I won’t go back to the old experience which is outdated and broken.