For reference:
Having to break a window before you can aim out of it, or having to dive through one during a game to take cover or advance won't exactly add realism, but perhaps a cool factor. Like glass it could be an eye hazard, but since everyone on a field is supposed to have eyewear, the only type of person affected would be someone breaking the rules.
This stuff could also make swat or hostage rescue types of games interesting too. Do you break a window to lure someone over or distract? Do you look for quieter means to the goal?
Either way, I intend to build some Thursday for fun to see how it holds up to my BBs.