I personally have seen the switch to a voiced protagonist as sort of an emphasis on the current trend for games to try to be more cinematic, rather than more about player imagination or things that require more investment in order to enjoy. Cinematic experiences are easier to enjoy when one has minimal investment into the game, whereas more roleplay/imagination-esque experiences tend to be more acquired through numerous hours of play. I personally don't play most videogames for the cinematic aspects, however. The most immersive thing any game can do for me is allow me to build myself into the world within the confines of what I decide to do/be, and a lot of that experience for me comes from NPC interactions, factional things, and experiencing the settlements and those therein in an in-depth and flavorful way. I'm definitely not a fan of most things that force me to sort of use a major template for the experience, where it's as if I'm playing a pre-made character that merely causes me to sort of watch everything unfold in a very... bystander-esque manner.
Part of me is also a bit worried with BGS citing that one of their main inspirations for FO4 was GTA V, considering that GTA has always had a very fixed protagonist. I've seen people argue that Fallout has always had a more fixed persona, and as I started the series with Fallout 3, I wouldn't be able to differentiate whether or not that is ultimately true. However, even with the pre-existing elements of Fallout 3, I felt still like a lot was up in the air. My main worry also would be that this is a sign of the times for what will come in the next TES game, in which I will be very dissatisfied if many of these ominous things being discussed (being locked out of dialogue after you talk to someone, only 4 topics for any given NPC, etc.) come true.