The idea of a "safe" list means newer guns can be forbidden because they're not on the list. Anyone who's dealt with California's "approved" list knows what I'm getting at, and it's a sneaky way to close the pool of available firearms in a few years.
+1, and worse yet, IMHO this could effectively quash innovation in the semi-auto pistol market, because manufacturers would be afraid to introduce anything really innovative for fear that their R&D money would be wasted if the ATF were to deem it an "assault weapon".
IMHO this is a similar issue to the FAA certification standards for new aircraft, which have long been accused of being overbearing as it relates to small and simple 2-6 seat prop-powered general aviation airplanes. Many such models on the new aircraft market are fundamentally a modified version of a design with roots in the 1930s through the 1960s, because it's easier, cheaper, and more straightforward to certify a modification than to take chances with something all-new.