Considering the open source nature of Letsencrypt, I wonder what the barriers/costs would be (theoretically) to a wealthy benefactor who wanted to duplicate its server side infrastructure and a core staffing level of persons, and fund a "parallel" equally trusted, alternative entity with a solid governing board. Same general idea how Acton funded the Signal foundation.

Somewhere that none of the physical infrastructure/hosting environment overlapped with existing Letsencrypt stuff so that the failure of one entity would have zero blast radius affecting the other.

I know there's a long and complicated process to go through to become a trusted root CA and get your CA public cert auto-installed in every OS and browser trust store. Indeed in the early days of letsencrypt I recall their root CA certs were signed by other older root CAs.