BruderSamedi

As you mentioned FO:NV, I have to admit I did not to have any companion on my first playthrough. What I missed here (and in many similar 3D-RPGs) when it comes to combat is control: I think you as the player should be able to directly control your companions, position them, make them use spells, and also level them up, so do everything to them you can also do with your main character. This probably fits into the "Combat/Challenge-viable" category. However, I am not worried about this point for P:E as it will be more similar to Baldur's Gate than to 3D Fallout in this aspect.