How would you let users know about this proxy without letting their government know about it? Instead of platforms like twitter, how about randomly giving out random proxies in some header that the app could query on cloudflare or google or akamai? Does Signal already make use of any CDN's for out-of-band signalling and fail-over? If the Signal proxy could expose an obfuscated load metric, then the CDN could pick ano…
That's the trick isn't it: having an entire population know something an oppressive government doesn't. Even if you teach everyone how to deploy their own servers, then that's the knowledge the government will start targeting. You can make blocks expensive, i.e. blocking other major, useful services that would disrupt society too much for them to want to deal with, but this of course has its own costs. It's censorshi…
That's not to say it's a free society or that censorship doesn't exist there, just that it's not the sort of regime that is particularly good at it.
If I had to guess, Iranian expats would be a likely set of people to start up proxy servers for their family and friends back home.