If open carry is constitutionally protected (and there's significant reason to believe that it is) then aren't the only restrictions on carrying contained in federal law? The exception would be those state laws that apply to open carry on their face and are "reasonable restrictions."
The school zone restriction is a prime example. The statute itself says that it doesn't apply to any constitutionally protected activity, such as carrying inside a motor vehicle. However, carrying inside a motor vehicle is only constitutionally protected as a byproduct of the constitutional protection for open carry, so the state school zone restriction should not apply. However, the federal Safe Schools Act in Title 18 should be applicable since state rights don't override federal laws.
Of course, this doesn't address the obvious argument that those who carry should play it safe, blah blah blah, but some of these restrictions (like the school zone restriction) can be defacto prohibitions on carrying at all in dense urban areas.