No they sadly don't have that, and that's the major issue of connectivity. All chat recipients have to be online/reachable to receive your messages, which is okay, but useless in mobile environments where you can't afford that constant traffic.

The broadcast type channels though are what the article talks about, they are great for off the grid and mesh environments.

Relaying and scattering traffic across neighboring peers (and handshakes via multicast DNS, for example) would fix a lot of the issues you'll get with Briar, but I guess that would imply a refactor of the codebase.

For these types of NAT breaking issues, a lot of protocols rely on STUN/TURN/TURTLE routing.

For my experimental software router I'm relying on broken firewall deep packet inspection, so I'm using exfil / smuggling protocols. Currently still works, according to my local setup of the great firewall (it's source leak was legit btw).