we still can't certify on an alternative port, DNS is not always an option and so there's people stuck with having to shut down servers while certbot does it's thing
[[ Ha, they got around to removing 115 from the list at some point, that was always funny. It got on the list because port 115 is in IANA's list as SFTP, but that's because IANA thinks SFTP means "Simple File Transfer Protocol" a long obsolete protocol like TFTP whereas the SFTP we know today uses port 22 because it's just SSH ]]
There's no intention to add more ports to the Authorized Ports list in the Baseline Requirements AFAIK. Control over other ports doesn't have a very strong connection to control over the whole named machine.
why are you shutting down servers to rotate certificates? a reload should be totally possible!
But with acme-dns, you just set a static DNS entry once and host your own DNS server solely for acme-challenges. So yes, it uses the DNS protocol, but the implications are very different from the normal DNS challenge option.