1) Maybe, but it would need a serious buff to be worth taking. It's not really worth taking as an ability, either.
2) No it shouldn't have any requirements at all. It's a flavor trait - why should it need requirements? "Realism?" In any event, the Source Hunters are NOT "normal people", which the main plot makes pretty clear, so an exception here makes sense anyway.
3) Shapeshifting was one of the things that was planned, but cut during development.
Please don't simply copy and paste things from a Fallout FAQ. Try to take a stab at providing an example of how it could be adapted to D:OS. What gameplay benefits does it have? Does it duplicate something that already exists in D:OS?