> Think of it as a similar model to ISRG and LetsEncrypt.

In that case it was started by an institution (mozilla) with a lot of heft in the area (mozilla's CA program is one of the most broadly used) and was backed by other orgs (google) that had a vested interest in it's success. I'd be interested to hear which potential sponsors you see in a similar situation here?

> rule of one person per subdomain

What is the plan to (without costly overhead or cost to the end user) validate who is an actual person? Even large corporations with loads of resources have problems with this without resorting to treating it as if a person equals a credit card number.