I was very late to the FO4 party so I'm not up to scratch on everything that has come out. If this is already known or has been discussed at length, blame the search function for not finding it .
Anyway, I was listening to an interview with Courtenay and Kal-el, and in it he jokingly said that sometimes he wished only one of the two main voice actors were super talented, because then he'd only have to play through the game 5 or 6 times. This puzzled me. Even if you had enough alternative dialogue you missed that would warrant another play-through, certainly 5 or 6 play-throughs seems a bit excessive. But what if the game has the same (or similar) lines recorded with different delivery styles, based on your karma, build, etc.? That would explain his comment, and would also explain why these guys spent so many years in the studio. It would also help explain why they decided on a voiced protagonist in the first place, when it seems to undermine their "be who you want, do what you want" motto. If both genders, between them, cover a wide gamut of personalities, then a voiced protagonist becomes much more desirable.
I am somewhat incredulous at the notion that a AAA studio would create so much content that would be mostly inaccessible on a first play-through, and also that they wouldn't want to divulge this colossal effort (particularly in light of all the criticism the voiced protagonist feature has received), but it certainly would explain a great deal.
Wishful thinking?