One interesting side detail: A Bethesda representative was demonstrating the combat and had power armor equipped. While he was basically a nigh-impenetrable tank, his visibility was cut down, so the perception stat had a significant penalty–one that made VATS nearly impossible to use[...]
I know there are a lot of questions on this issue, and there’s only so much I can say, but I will say this:
Giving any kind of specifics right now is a bit of an exercise in futility. I could tell you what the stats on the Power Armor are at this very moment, but then you’d get the game in a few months, see that they’re different, and consider me a filthy liar.
The truth is, we’re in the stage of development now where systems are getting constantly balanced and rebalanced. So Power Armor will certainly affect your abilities in some capacity, but exactly what it modifies has changed, and will likely change again.
Though I will clarify one thing — nothing flat out prevents you from going into V.A.T.S. Some armors grant different bonuses and penalties, and that can affect your Action Points (and certain weapons certainly require more Action Points than others). But, as it’s the player’s job the manage this stuff, using V.A.T.S. (and using it effectively) is possible regardless of what you’re wearing.