I've been thinking along similar lines but in a totally different direction - and have a theory that is just begging to be shot down - iris diaphragms. I've located a manufacturer of high-temp iris diaphragms that have max apertures of 90mm and 102mm. Their standard products aren't geared for automation, instead they just have a big lever sticking off to the side. But, they do make smaller models that are geared and I'm hoping they might be able to make the large ones geared too, either that or maybe some sort of stepper motor could be attached to a shortened lever.

I'm thinking you get the benefit of truly blacked out headlamps plus the ubercool factor of them being able to open and close like real eyes.

I still have to get on the phone with those guys down in RI who do custom headlight assemblies. I'm sure if anyone can tell me that the iris approach isn't feasible it would be them...

Here's the link the irises in case anyone wants to look:

http://www.wilkes-iris.com/index.html?lightingmain.html