Oh that is really smart. Is there a way to build a simple DNS server into a certbot (or other client) plugin? That DNS server doesn't really have to be available outside of the verification time window.
DNS validation has been a thorn in my side for a while. Not only do I use DNS hosts that don't have APIs (like Google Domains), I also don't really want to give every web server access to my entire zone. That seems like a huge attack surface.