This would be a terrible idea. As it stands already, AT/AA guns are massively vulnerable to tanks, planes and arty, and already take a good minute to repair as it is. And in that time, you can usually expect a plane or tank to return anyway, usually scoring an easy kill. And that's assuming an arty bombardment hasn't destroyed several guns/mg's/radios all at once... damage that would take a number of engineers many minutes to repair.
As it stands now, manning AT/AA guns is about the worst job in the game. You spend half your time repairing things (speaking of which, anyone ever seen anyone get more than 2 repair points?), and the other half generally being slaughtered by planes/tanks/arty. Why would you want to make it even more unbearable?