A lot of Let’s Encrypt is not the software but a bunch of auditing and process that ensure compliance and make it legible to the required auditors.

I understand there's probably a big thorny problem of duplicating the corporate process/policies on the human level that ensure compliance, but is the back-end software pipelining stuff to CT logs not also something that can be replicated? Or is it not part of the server side stuff which has been open sourced?

https://letsencrypt.org/docs/ct-logs/