My other idea is if wearing heavy armor you cannot swim, or any other npcs and enemies. Or perhaps if your strength is high enough you can. This would be super cool if enemies drown as well, which I don't remember if they do. Anyway, just a thought.

I really don't think anyone could swim in any armor, light or heavy, at least not effectively. It's hard enough to swim with just street clothes on.

However, yes, people who wear armor tend to stink, because armor does stink, and you can't really wash it. So, your saying you want PC's Charisma or Personality or Speech to be reduced when wearing armor to simulate the adverse smell they give off?