Would this be useful to people in countries like Iran, where the internet is restricted and completely cut out whenever the government needs to shut people up?
Assholes will opportunistically shit on anything that isn't too difficult for them to worm their way into. Crapping up DNS by making all unknown domains resolve to an ad server? Sure. Making unencrypted HTTP unusable by inserting ads and blocking keywords? On it. Blocking any port they haven't heard of? Hey, who needs ports 70 or 23 anyway, am I right? Assholes can be state actors in a state which doesn't go to extremes censoring the Internet, or they can be companies or other institutions with assholes dictating IT policy.
Fanatics will poison BGP to blackhole YouTube and, if it knocks out YouTube for a couple neighboring countries, well, those countries either agree with them or are kiddie-porn-hacker-atheist-terrorists who need to be put in their place by Morally Righteous Leaders anyway. Fanatics will kill anyone who sends or receives encrypted messages the authorities can't read, just on general principles.
HTTPS and maybe some tricks with DNS will protect you from assholes. You need legitimate tradecraft to thwart fanatics, and even then you're rather likely to be killed by a government that really doesn't care enough to even stage a convincing accident.
But how exploitable is IPv6? And/or how exploitable are the critical pieces of Yggdrasil infrastructure?
Cell phones are popular with drug dealers in south america because they're impossible to shut down - if the government can't shut down drug dealers, they definitely can't shut down people sharing offensive memes.
They'll just shut down every cell tower within their borders. Iran is already willing to impose full internet blackouts (https://en.wikipedia.org/wiki/2019_Internet_blackout_in_Iran).
Drug dealers are an annoyance but they aren't a direct threat to any government (as long as you let them be in peace). If it's a direct threat to you, then you do anything, even if the benefits outweigh the risks.
https://www.washingtonpost.com/world/asia_pacific/after-two-...
They're impossible to shut down without (potentially) affecting innocent bystanders. If they don't care, they absolutely can and do shut down towers.
In this case, if they judge anyone broadcasting or using this network as subversive, then there are no bystanders, only accomplices. And, thanks to the tyranny of the inverse square law, it becomes much easier to sniff out broadcasters/uplinks as well.
The easiest way to mitigate this is to do both -- rebroadcast a cell connection over WiFi, and do so intermittently and in varying locations to complicate triangulation.