>This seems pretty doable from a tech standpoint. Is funding really the only reason it's not being done?

It's not being done because this already exists. It's called 4chan (though 8chan is a better fit; I don't recall if source code for it was ever made available).

Of course, 4chan depended on a single individual's pocketbook and liberal moderation policies, which has let it down in the past; having such a service be government-funded and shardable so that if one mod goes bad you still have a place to go would help.

But at its core, you'd still have 4/8chan, because that's what "public access" (and "free speech") means. And while it is very valuable, a lot of people just can't properly digest it.