I feel this is somewhat of a non issue, play the game co op with more than one person, and for this example I will use friends you know irl, or have played with and spoken to often. I've already seen responses I did not expect from people I've known for quite some time and I know they are picking choices honestly as near as they would be able to in a manner similar to real world interaction if they were placed in these situations. This to me adds a great amount of depth to the game itself. I think that was the primary concern for the way the game has been laid out, at least linguistically. I mean come on, the co op part of it has been a big deal but people seem to throw it out the window and not add people they play with ( or might play with) into the equation.
I get where people are coming from in that they want their own individual character to start reflecting the choices you've made in their personalities, but it seems empty to me as that would remove thinking about your actions over the course of the game in any significant manner, you're expecting things to turn out in this or that fashion, and that right there would stomp on a lot of the freedom of development they are aiming for.
Just an idea in any case, feel free to hate on me if I was unclear or didn't address the issue in a manner you find more appealing, I'll try change my stats to suite your needs in the future ( just tell me what I should be acting like by the end ok?). A little sarcasm I guess, I just figure we're thrown into 2 characters who are already the people they have become over whatever life they had before we jumped in and took control, realistically we wouldn't see major changes to their behavior in the short amount of time we have with them would we?
In summation, I find a lot of their interaction to be pretty similar to what I've noticed in a fair few soldiers and mercs over the years, light in communication to each other but it does hold a certain depth that is hard for them to translate over to one another. At least that's often how I end off communicating with people these days.