http://www.youtube.com/watch?v=juMWKWR_BCo It was done fantastically and I would love something like this to be done for helmets in skyrim. Just obstructing enough that you might want to take a helmet off when you enter a city, but not enough to actually be a disadvantage for you in battle.
Okay, I have to admit, that was pretty cool. Not just the visors, but the whole thing as a whole was really cool.
I'm all for having it as an optional feature, but it's way, way down at the bottom of the list for priorites, this sounds to me like something that's best as a mod honestly, svcks that console players who want the feature miss out, but Bethesda has many more important things to do.
I wouldn't use it, but I would welcome the option regardless.