There was some discussion about Let’s Encrypt providing a similar service in another thread: [Suggestion] Let’s Encrypt operated, TXT-only DNS Hosting for DNS challenges
Some of the discussion there is probably relevant to your idea as well.
There was some discussion about Let’s Encrypt providing a similar service in another thread: [Suggestion] Let’s Encrypt operated, TXT-only DNS Hosting for DNS challenges
Some of the discussion there is probably relevant to your idea as well.