California, until recently, was operating under a bastardized variant of this concept: open carry was legal if your gun wasn't loaded. While allowing only the carry of an UNloaded weapon probably would not meet with success now that the SCOTUS has ruled that the 2nd Amendment is about self defense, that was California's law and the state would no doubt argue that they hadn't banned carry, only regulated it.
But now they've eliminated the escape clause allowing the open carry of an unloaded firearm. So now the California "may issue" permit system is ripe for challenge.
Indeed, the district court judge in 'Peruta' cited reliance upon the non-prohibition of (neutered) open carry to meet the constitutional burden.
The good thing is that she (Judge Irma Gonzales, IIRC) at least thought there WAS a constitutional burden. Not a year later, the CA legislature banned the form of carry upon which her ruling relied. It's on appeal now, Should be interesting.