It would be ideally integrated with some LJ client or other, but would not hit LJ for the actual communications stuff, only use it for userid/password authentication, and then, erm, something. Where someone else's computers do the whole "Hi, how are ya? Let's get data from one place to the other!" aspects of the chat.
But it would generate easy-to-post chat logs, with a default setting of Private for the chat logs, no matter what the default setting of the journal was.