I have some experience with using Pis as hotspots on communities. The wifi range is very short and it won't handle more then a few connected devices at a time. Which sould be enough for a small village, but would require to be connected to a router if more users are to be expected.
Good thing is that we have a good part of that work done with the p2p hotspot, which includes a ssb-go-pub, wifi, and captive-portal for 64 bits devices: Pis 3, 4 and Zero 2.
I'll buy a few Zero 2's to test while I'm in the US, also curious to know if they'll handle ssb. With NodeJS stack we won't be stuck to 64 bits only devices, and @andrestaltz's experiments show that there isn't a significant performance gain by changing languages.
I absolutely love the idea Mix, much easier then building for Android, solves the offline problem and helps with discovery. There's addtional harware + energy barrier, but can be minized thru aiming for low cost, energy efficient devices or simply putting an existing device to use. Even old/damaged phones can be used by running ssb on termux and creating an AP, captive-portal would only work on rooted device.
For syncing wifi-connect can be used, so that one Pi can connect to either the Internet or to another Pi's hotspot. That way someone can take the Wiki device to town everytime a sync is needed.
This should be enough to check if the UI concept is going in the right direction. This gives breath for a next round of funding where a native app could be worked on.
I'd be able to contribute to the project by setting up all the non-ssb related software to run on the Pi, since I expect it'll be mostly adapting the P2P Hotspot project.