They did it once before. The umpire had a camera attached to his hat. It was pretty cool. Not sure why they stopped.
Actually I'd like to see the QB Helmet Cam again. I recall watching Kerwin Bell getting blasted by a pass rusher in the WLAF. You could see him making his reads, the rusher getting closer and closer until... his head goes flying back and all you see from the cam is blue sky. Made me realize how little time a QB has to make his decisions and get rid of the ball. I couldn't find a film clip. This is the best I found- http://www.worldleagueofamericanfootball.com/id151.html