Distributed chat systems only are advantageous because you get away from having centralized servers, but you still have a bootstrap problem to get everything up and running.
The only 'unique' thing that Bittorrent can provide although is execution, delivery & a tendency to open source their work. They have shown they can deliver by implementing usable bittorrent sync clients for the major 4 OSs (Windows, OSX, iOS, Android). That usability alone would increase the amount of the internet using encrypted communications significantly, putting a major hinderance on dragnet surveillance.
Hell we might find out that bittorrent chat uses libOTR once your in an actual conversation, since they did all the hard crypto stuff already. They'll just be adding a P2P discovery layer, since that is what they are actually specialized in. That is what I would do if I were them.
There are no usable open source OTR or PGP clients for all 4 OSs still. ChatSecure for iOS still crashes a lot. Adium/Pidgin is pretty much the only usable OTR client I know of, and they are desktop clients.
They would know:
Who talked to who
How often they talk
When they talk
How much information they exchange
Their IP addresses
In fact, the only they wouldn't know is precisely what was said, but that's often a very small, non-critical piece of the puzzle.