Meteor works on top of a traditional backend (typically MongoDB afaik?) to give you full-stack reactivity.

Jazz implements essentially a distributed database with permissions based on public-key cryptography, so you can meaningfully create, edit, share and store data on the client (even while offline), which gets synced to other users and devices (and stored in the cloud) whenever you're online

Is this synchronisation (theoretically) possible over p2p communication protocols like Bluetooth or wifi direct?

I would more than love to have local networks that can be emergent and growing and shrinking in this way.

Reminds me of my student days when I was traveling in the train, wondering why we couldn't have a p2p social network for people who are in this train _right now_

yes! The hard part that Jazz doesn't solve is peer discovery. If you give Jazz a peer and a transport mechanism it will happily sync to it