why I proposed http-25 challenge was it already allowed on BR so LE can do that which BR change.
if we are considering authorized port change, how about port 115(which was mistakeing simple ftp for ssh sftp), which was authorized port in BR until 1.5.1(SEP 2017)? (https://cabforum.org/wp-content/uploads/CA-Browser-Forum-BR-1.5.0.pdf)