That only creates a link between SSH keys and a domain; It's even worse than relying on GitHub since you have to trust that multiple account haven't been hacked (registrar + DNS) and that neither the DNS host nor the registrar are acting maliciously.
I agree. DNS is its own bundle of insecurity.
Psst. Github has all that stuff too. Just more because it is a growing and changing webapp instead of an ancient, solidified key value store.