The biggest problem I immediately foresee is that this sounds backwards. It doesn't work best in areas with patchy or no internet, it works best in areas with lots of participating devices. It's most needed in areas with patchy or no internet, but those areas are likely to be the opposite of the areas with lots of participating devices.
I would say that the underlying issue is that people do not really "own" their devices and the corporations that do are vulnerable to (or complicit in) state coercion.
You cannot truly have freedom on a non-free device, you can just be small enough to not be worth taking action against yet.
For a more extensive discussion on censorship resilient mesh networking, see IETF Internet Standard draft from 2012 [1]. After the Arab Spring there was global hope. Great to see revival of this topic today. Mesh networking is 1990s. The lesson from decades ago was that mesh networking can't be the killer use-case. Users need a reason to install this and allow it to drain the battery while looking for nearby nodes. Mesh networking never broke through the glass ceiling.
Blocking apps is real. Even Amazon killed a side-loaded app [2].
[1] https://www.ietf.org/archive/id/draft-pouwelse-censorfree-sc...
[2] https://torrentfreak.com/amazon-remote-disables-piracy-apps-...
But I mostly agree - they rolled it out worldwide later on because once you reason it through, disabling it when it's not actively used turns out to be the better default.
I think you could reasonably argue that the measure limits Airdrop spam.
If there is a low density area between two people, a message could take a long time to show up. A message from NYC to LA is effectively relying on the messaging being cached on a phone in NYC, that person flying to LA, and then continuing the journey.
Those working against the demonstrators could send people out with QR code to infect the phones will malware for their own means.
On a Pinephone you can turn it off with a physical power switch.
If you really wanted to, on most other phones you could desolder it and throw it in the garbage. You'd need to already have custom firmware on the main CPU (or should I say "application processor" to fit in with the people who say "baseband processor") so it wouldn't crash or lock up when booting.
A little bit less destructive (in case you want to use your cellphone as a cellphone later) would be replacing the antenna with a dummy load.
Wireless internet is getting better, but when you really need something like this, you really need it.
In fairness to op, the proposed solution seems best intended for comms blackouts in densely populated areas rather than areas with persistently limited access.