Thank you, this draft is literally perfect and I wish we had this years ago. Most people don't know about acmev2 account rekeying either. It is great you decided to use account uri instead of public key thumbprint.

Recently I wrote a simple acmev2 tool specifically for manual upfront acmev2 account creation, rekeying and getting TXT records on stout for dns-persist-01:

https://github.com/pawlakus/acmecli

It also helps with stateless http01 printing thumbprint...