I really hope they keep New Vegas's style of the companions having their own styles, ideologies, backstories and loyalty missions. Although some of 3's companions were interesting, I didn't care about them anywhere near as much as I did for New Vegas's companions. For example, lets take Codsworth. If he is nothing more than a robot (the old family butler) then I don't see him as much more than a glorified pack mule. However, i would care a lot more if say, it was discovered that Codsworth is eligible for an upgrade. By finding the correct components and saving an engineer who is familiar with pre-war tech, we could upgrade him to an enhanced domestic robot butler (Greater carry weight, maybe a workbench function). On the other hand, we could also convert him to a Mr Gutsy type robot and weaponise him, making him more useful for combat.
Little things like this would make a big difference in how I see companions, and I really hope they keep this sort of stuff in.