For me, I wish we could meet Bill Calhoun, the surviving FotA that accompanied Caesar and DIDN'T join the Legion. I dunno why, just sounds like an interesting guy. He's a FotA so he's probably a nice guy and he stood by his morals at the risk of facing the wrath of Caesar, yet was luckily chosen to be the surviving messenger. Not only that, he managed to return to the Mojave on his own. Sounds like an all around BAMF. He could've been the player character in a Fallout game ffs, and it sounds like he would have interesting insight to Caesar's character, interesting experiences and interesting opinions.
As for existing players I wanna hear more from, first there's Mr. House and the King. Why? Simply because they're probably two of the most interesting personalities in the game. I'm not exactly DYING to know more about the King, but rather I think he just has the potential to be interesting no matter what you discuss with him. As for Mr. House, it's more I want to know more ABOUT him. House is a frustrating character if you're trying to decide to ally with him or not, mostly because you're given VERY little info about him from other people. You only have your very limited convos with him where he seems intelligent and on the ball, and most importantly, he's incredibly interesting and has accomplished great feats in his lifetime. Hell, House may be -the- most powerful character in the entire Fallout series, if you look at what he's accomplished in life. But then you walk outside and hear almost no one speaking highly of him (think Majorie and Swank are the only two who will), and yet those very same people rarely ever justify WHY they hate him. Ok, he apparently forced a lot of people out of their homes and there was a lot of bloodshed when he took control. That's a big deal, but there's nothing more? Nothing good to say about him? Nothing else bad? With House, I always get the feeling that I'm missing something, because I only SEE good and progress, but I only HEAR bad things, albeit with no actual justification 9 times out of 10.
Another character is Lucius. Why? Because we all know Caesar likes to keep his followers in the dark. He keeps them ignorant and out of touch with the reality of things. Lucius however? The game seems to imply that Lucius is -the- Legionnaire that Caesar actually tells some truths to. I'd love to hear his opinion of some of these things, but sadly he only talks to you to give you updates or orders and isn't open for actually discussing them. I mean, in the same way the Courier is interesting to the people of the Mojave for being the guy that has access to Mr. House, Lucius is the guy that has access to Caesar in a truthful sense. So yeah, I'd like to hear more from him.