The NV hardcoe mode only tells a portion of the story. Two of Skyrims most popular mods are survival mods: RND and Frostfall. Many of the features that are being added, or have been added to Skyrim in the past, seem to have been inspired by the modding community. It really shouldn't come as any surprise that someone in the studio would look at those mods and wonder what they can do to implement them.
Beyond that though, I share the opinion that it should have been there from the start, but not because of hardcoe mode. hardcoe mode was a tacked on feature to NV. Survival mode, IMO, makes more sense here because of design choices that BGS made when developing FO4. For example, the emphasis on settlements. In the base game, the use of approximately 30 settlements in the Commonwealth feels like BGS simply got way too carried away with their basebuilding feature. A lot of people complain that there isn't enough variety to them, and it gets very grindy. However, if you add weight to nonweighted items, like caps, meds, and ammo, those settlements are less of a feature that you can simply skip and an absolute necessity if you don't want to trek across the Commonwealth without fast travel. The foot and water mechanics that settlements provide also make more sense when they actually provide a tangible benefit to you.
Other design features also make me wonder why these changes weren't in there in the first place. For example, if there isn't a functional difference between a sleeping bag, a mattress, and a bed; then why bother introducing all of them? From the perspective of the game's economy, sleeping bags are superior because they require less resources to make and there isn't a true difference. Once you add in the features from hardcoe mode, the progression makes more sense. Sleeping bags are easier to make, but don't provide a "good night's rest". You'll need an actual bed to do that. The same thing is true of the transportation options as well. Without the new survival mode, the vertibird grenades that are provided by three of the four factions are entirely unnecessary. They don't really do anything that couldn't be done a lot quicker just by fast traveling to that location. They make a LOT more sense when fast traveling is removed from the equation.
All in all, I feel that it should have been there from the start because a lot of the ingredients for developing it were already there. That wasn't true of RND or Frostfall, which had to add scripts and resources to make them playable.