The problem is, an Article V convention doesn't negate the requirement for ratification. Whatever you come up with has to garner an enormous amount of public support or it fails.
With pot, it's like JoMama said, it doesn't need a constitutional amendment, it simply needs to be enacted into law by congress. It could probably be effectively decriminalized through DEA by executive order.
I've felt like for a while, this is the best way to go about it, kill the federal drug classification and decriminalize it. With all the states now having pot statutes on the books and up and running, I expect to see a case come before SCOTUS soon. You simply cannot prosecute me for a felony in Alabama when my action is perfectly legal in Colorado. This is what "equal protection under the law" is all about. Sooner or later, someone will bring the case and the SCOTUS could rule federal marijuana laws unconstitutional.
I think you are wrong about this Boss. Equal protection is not about laws being the same in each state but rather about people being treated the same and not having laws apply differently based on a particular characteristic of a person. Even then there are exceptions, as not all characteristics are protected; a felon may be arrested for owning a firearm, for example, where a non felon is not.
There are certainly laws which apply only in certain states and not others. Age of consent laws differ from state to state as an example. It may be perfectly legal to have sexual relations in one state that would lead to criminal charges in another.
Now, if medical marijuana laws only applied to, say, people of Iranian descent, that would fall under equal protection.