They already exist. When you look at some of the overt armor that was/is used by the military--particularly the BALCS armors--the full kit will have shoulder/upper arm coverage, a high collar, and a flap that covers your lower abdomen. While these are mostly to protect against fragmentation, they should stop all handgun threats as well. Outside of GWOT and some SWAT teams, that kind of armor isn't common though, because it's bulky and very restrictive.
Oh, and a hit directly to the balls is gonna rupture a testicle anyway because of backface deformation. :)
No clue, since it doesn't seem to stop you from getting NFA items approved.