The implementation is open source. You can launch your own ACME server (valuable for testing), and use that. CAs implementing this technology obviously need to go through the same hoop-jumping in order to become trusted, but that's true of any strategy of starting a CA.
The technology is available for any CA, existing or new, to copycat.
And if they don't want to use the open source reference implementation, they can cleanroom an ACME server that works with all the existing clients that work with letsencrypt.
The technology is available for any CA, existing or new, to copycat.
And if they don't want to use the open source reference implementation, they can cleanroom an ACME server that works with all the existing clients that work with letsencrypt.