A nonbinding convention can be called without the 2/3 of state legislatures...however, as you pointed out, it would eventually have to be recognized by 2/3 of the state legislatures and ratified by 3/4 of the states to be constitutionally-binding. So you're right in that respect, that it would be extremely difficult to enact the changes. However, since a nonbinding Constitutional Convention can be called without that 2/3rds recognition...if it's multipartisan and based on good policy, at that point, it would be a matter of putting public pressure on state legislatures to recognize whatever comes out of the convention itself.