I agree that I hope something a little more seamless will be done for this, but I'm a little confused by this statement: "maybe press 'L' to sort of follow the conversation."
Why "sort of"? As far as me and my buddy can tell, following the conversation via the journal works perfectly fine. It's updated live as the conversation progresses and includes the player's choices and everything.
It would be nice if you didn't get yanked out of it when a co-op choice appears and it all happened in one screen.
It would also be nice if you were somehow notified when your partner had entered conversation. Perhaps have a shortcut key you can press to open directly to that chat dialog in the journal (or a new dedicated window just for this purpose).
But for now, until a better/more seamless solution is added, the journal appears perfectly functional. You just have to let your partner know you've started a conversation so they know to manually open the journal. Am I missing something about the journal?