There is a global syncthing discovery service. Nodes can locate each other by ID using that service. The code for that server is open source and you can run you

There is a global syncthing discovery service. Nodes can locate each other by ID using that service. The code for that server is open source and you can run your own on your own network. Individual nodes on the same subnet can discover each other without the discover service. You do need to know the node ID and repository ID, and the nodes both need to establish that relationship. But the mutual acceptance of the node ID is how trust is established so I don't see how that could be made optional. They could allow for UI improvements where the user is prompted to add a repository that has been published from another node rather than requiring that to be manually added, but that's just a ui change. I haven't used btsync so I'm unclear on what specifically is missing on syncthing in this respect. It seems to be pretty good with respect to discovery.