> There’s also nothing stopping them from building Signal clients such that they’re able to directly connect to each other over the local network and do whatever transfers are required that way.

There's also nothing stopping you (or anyone else here) from adding such a feature. Either into the official, Molly, or one of the other forks.

You may also be interested in this feature request.

https://community.signalusers.org/t/signal-airdrop/37402