I believed DDNS-API solution (Docker) should be workable for you. And below comments just tells what I'd like to share, with no offenses.
I agreed but not all to this point, actually... there might be some out-of-control issues, when someone wants to get a special name, like [name].myunraid.net, it's not fair to others who wants the same name sometimes... Or...someone wants a different name instead of the username of this forums. BTW, as we know, we can access to My Server Plugins page and then access to our unraid server by clicking 'local access' or 'remote access', no need to remember the address [ip+hash].myunraid.net, so I think DDNS-API solution of which a domain that owned by end-user, or the automatic generated [hash].myunraid.net should be more equitable.