As a fun project, why not.
But this is just another problem which can be solved by radio bought from aliexpress.
No wait, let's reinvent the wheel again :)
In case of war or something, internet is down, decentralized Bluetooth messaging app is your last problem.
IRL you will be using unencrypted radio, yes doesn't make sense. But already proven in the UA war.
Try using encrypted radio on the frontline and you will get suicide drones or artillery shell on your position, pretty quickly ;-)