This is a well meaning, but deeply flawed idea if you like the idea of the Second Amendment protecting a 'normal' right. If you believe that so-called assault weapons are protected by the Second Amendment, why subject the exercise of that right to a popular vote? Just on principle you'd be depreciating the Second Amendment's status as a fundamental right. Fundamental (and enumerated) rights stand above popular acceptance.
By that same logic, some southern states would have been able to re-enact Jim Crow laws based upon popular sentiment. This is a very bad for many reasons. The opposition likes to try and make this a popularity contest. Ballot initiatives designed to protect rights only serve to make rights subject to prevailing popular sentiment.