This has nothing to do with parked domains. I mentioned 'similar to parking' because what cloudflare tries to do is basically a way for the website owner to earn income passively (like we do in domain parking).
Imagine how many crawlers hit websites every second; now, imagine if they actually paid to be allowed to crawl those websites.
If I'm not mistaken, there is a 402 Payment Required status message that, potentially, will be used by the website owners to decide whether a crawler is allowed to go about its business or not.
Imo, if this goes through, it will be huge. But as I said, probably it's only me that sees this as a huge future development lol.