> again submit their transactions containing any speech they like using again VPN/Tor and not interacting with those wallets with any KYC-enabled exchange.

That last part seems like the key challenge to me: what you described isn't cheap and it only works to the extent that you can do business with people who aren't following KYC. That makes it more likely that the entire service will be tainted because the non-trivial cost means that people aren't going to use it if they don't need to.

The other problem is that durable records are inherently risky. Your use of such a system isn't just a question of whether someone can see the transactions immediately but whether it'll retroactively become de-anonymized — the public blockchains are right out there but if you're trying to use a private L2 system you now have another party you're placing a lot of trust in — not unlike the questions about how you'd be able to trust a VPN provider or Tor nodes not logging your traffic.