The problem here is just if Obsidian want to include an half baked TPP.
Among the already mentioned issues like animations, clipping, etc., you guys need to think that the enviroment and closed spaces maybe are not designed to accomodate a camera following the player.
If the release is scheduled for 2019 they would be forced to a partial redesign of a significant part of the game, and maybe even DLCs, to add a feature that would drastically affect the development, the release date and that maybe wasn't even considered from the beginning. Or was considered and discarded, who knows.
It could be patched in later on after the release but it has to be seen if would be worth it.
However until the implementation of an optional TPP camera can be done within their budget and without compromising too much their vision of the game I see no reason not to include it.