I don’t see it happening in a reliable way, but I could see it as a best-effort solution. If the assumption is made that the majority of users run certbot from one machine, then certbot will be aware of all certificates issued by a user, theoretically, and can display warnings based on that. It falls apart if someone uses alternate methods of issuance or has multiple servers running certbot for the same or different domains, but it is better than nothing.
That being said, I’m not sure I like how hackish it feels, and the possible false sense of security it could engender. If someone running certbot on multiple machines is relying on the warnings rather than reading up on rate limits, they could start hitting those limits through, arguably, no fault of their own. The argument there being that the warnings imply a level of safety that isn’t actually there, whereas the lack of warnings impart a responsibility on the user for their own avoidance of rate limits. In the end, I don’t think it would work out as well as intended without a more reliable method for determining issued certificates.