I assume they'll eventually release a technical specification that allows other clients to interoperate. I think it's better to get the usability right and other aspects polished first.
I love BT Sync! The current client is not so bad, it's easy to use. I like how it's easy to port your config from one computer to the other with dumb text file. I'm just curious, what do you think is missing in it?
..and it is the best solution for guaranteeing confidentiality and the encryption need/problem - not to need it, since there isn't a server to eavesdrop on