It took me like 12 days to read the whole article, so, this comment is super late but someday maybe you'll run across it. All I want to say is that's a great idea. Back when email started entering wide use I was flummoxed as to why the post office didn't offer its own email options.
Thanks for engaging with the discussion. With respect to the thought that came to you back in the early email days, I don't mean to be pedantic when I say this, and it may have had definite merit — like ensuring services that are naturally monopolistic due to network effects, are provided by an entity collectively controlled by the public — but an email service wouldn't fit the economic definition of a public good.
An open source codebase allowing anyone to set up their own mail server would be the public good in that domain.
A table that gives examples of private vs public goods:
For more complex goods, involving management of platforms, I think the only type of public good that could compete with proprietary offerings is the software that allows people to form a decentralized consensus and run applications on top of it, e.g. blockchain node software and smart contract code, respectively.
