Maybe it's because I remember when ISPs where fly-by-night operations with a bunch of modems spread on office tables.

You say it can't happen again, but IMHO that's not true.

It happened before because at that time the government(s) didn't give a damn.

Not true anymore.

Of course that exploited the pervasive POTS network over which we could tunnel ISP traffic.

What is the replacement? Mesh wifi? Guerilla fiber deployments? Or just a bunch of VPN tunnel brokers trying to evade blocklists on the corp-approved ISPs you have to keep using in place of POTS?

yep, I think it is a miracle that we can still reach almost any IP from any other one. Only a matter of time until this goes away imo. I‘m already increasingly forced to bounce around VPNs to access websites from different countries

Future routing protocols (already under development) that include end-to-end route verification will be the end of it, I expect. "Democratizing" part of the Great Firewall and building it into the 'net itself. Only way around it will be proxying, and that'll risk getting the proxying-IP partially blocked, if it's caught or any of the traffic is deemed "bad", and requires that you can route to the proxy itself in the first place. Won't be entirely immune to circumvention, of course, but will make selective and region-blocks and throttling more common and more precise, and significantly raise the bar for getting around it (which'll probably be illegal nearly everywhere, too).

There are already a lot of community driven meshed networks all over the world.

It doesn't really take over because so far we are pretty much free to do what we want from our ISP connection. Some countries impose dns censorship but appart from the few dictatures that run their great firewall, it is light censorships as they let people query the DNS server they want.