The title says it all really. No power armor inside interiors and when the player tries to enter a cell with power armor they will receive a message saying "You can't enter with power armor" or something of that nature. Something simple in concept, but I have a feeling there's a lot more scripting behind it all. Anyways, it's an immersive gameplay change that would make me use power armor in survival. I'm currently working on my own mods, so I won't get to this idea for awhile.