> preemptively finding such proxies and jumping between them
This is why it is so important to create protocols for communication instead of single-point-of-failure services. While it is still possible for bad actors to interfere with traffic, it is much harder to shutdown an entire network of federated servers. In contrast, a service can be disabled by simply throwing legal papers at the person running the service (or otherwise threaten them, bribe them, etc).
> DPI could drop packets containing emails addressed
Which is why that email should have been encrypted. Even non-authenticated opportunistic encryption would make that kind of DPI much harder and more expensive.
We've had encryption for a long time, and there is absolutely no excuse for to not have encryption in all network software. Unfortunately, a lot of software has been badly negligent in their duty to keep their users safe.
> cuts off the country's Internet access entirely
...they should be left with a split network, still able to communicate internally. It is pure hubris to believe that a single service will always be available in any situation; when international links are involved, some amount of loss-of-service should be assumed. This is why email allows multiple MX records - servers fail, so build in backups, some of which can be local.
> peer-to-peer stuff
Yes, though the model to copy is federated services like email.
The power of the internet is that it IS peer-to-peer. No 3rd party has to grant authorization to listen(2) for connections or connect(2) to a remove host. This has been forgotten because of the damage that NAT does to the network (you aren't a full citizen ("peer") on the internet when you have to ask the NAT device to forward your packets.)
Now, after about a decade of failing to heed the warnings about NAT, the digital imprimatur[1] is being constructed and running proper peer to peer (no 23rd party) is harder than ever. Hopefully IPv6 can reverse this trend.
[1] https://www.fourmilab.ch/documents/digital-imprimatur/