This is a great idea, well done! I think as a next step you should look a bit more into routers themselves. You can flash them with an opensource os like openwrt [1] and run a chat (or some kind of communication) server on it so everybody connected to the same wifi can freely exchange data.
This way you can turn any wireless capable [2] machine into a small community network.
> great use case I've seen are college campuses where thousands of students connect to the same WiFi,
This is indeed a great use case. Right now you're only thinking about chat but its got more applications like semi-remote teaching,tests ,role calls etc. But (I think) its far easier to realize it if you work at the network level rather than at the app level.
This way you can turn any wireless capable [2] machine into a small community network.
> great use case I've seen are college campuses where thousands of students connect to the same WiFi,
This is indeed a great use case. Right now you're only thinking about chat but its got more applications like semi-remote teaching,tests ,role calls etc. But (I think) its far easier to realize it if you work at the network level rather than at the app level.
Best of luck!!!!
[1] https://openwrt.org
[2] router, raspberry pi, laptop, your phone