"Time" is measured in combat by action type. If you can reload a gun as a free action, it takes no "time". If it takes more than a free action to reload they're only reloading one gun (or barrel, if it has more than one) per action. That's a very poor justification to use to change the rules. This was already covered (by the rules) by free action limits.
Again, rules forum, and the rules say "at least one hand free". More specifically:
Loading a Firearm wrote:
You need at least one hand free to load one-handed and two-handed firearms. In the case of two-handed firearms, you hold the weapon in one hand and load it with the other—you only need to hold it in two hands to aim and shoot the firearm. Loading siege firearms requires both hands, and one hand usually manipulates a large ramrod (which can be wielded as a club in combat).
It says "at least one" because siege weapons require two.
Your suggested rules change would cause all sorts of other problems. Juggler bard, vestigial arms, prehensile tail (not positive on this one), off the top of my head. I'm sure there's other ways to dual-wield guns and still reload them. Ways which currently work, that your change would invalidate.
