You don't need to hold physical cash to hold USD. You could have a bank account in London, Geneva, Paris, or New York with your pounds, franks, euros, or dollars. If you need to leave the country, your savings are already outside of it. Just like your bitcoins.
The answer seems to be that repressive countries haven't yet put in place effective mechanisms to be repressive with respect to bitcoins. But there's zero reason intrinsic to bitcoin to expect that to continue. On the contrary, since everything is digital the choke points are easier to control, not harder.
"Much less from Iran" misunderstands the problem with opening an account from the US. Swiss banks don't want to subject themselves to the long reach of the United States government's aggressive criminal justice system. That's the reason they won't open a bank account for a US system anymore. See, e.g. https://www.swissinfo.ch/eng/tax-evasion_us-programme-nets--...
The reason it was impossible, until recently, for an Iranian to open a bank account in Switzerland was not because of the Iranian governments, it was because the Swiss bank was afraid of running afoul of the US sanctions regime. Because those sanction have been lifted (at least for now) an Iranian can open a bank account in Europe, albeit they'll still have to go through a fairly extensive KYC process.
The answer seems to be that repressive countries haven't yet put in place effective mechanisms to be repressive with respect to bitcoins. But there's zero reason intrinsic to bitcoin to expect that to continue. On the contrary, since everything is digital the choke points are easier to control, not harder.