Im not sure how they want to do the 16th but they want to do the 17th the prescribed way. Sure its within the limits of the constitution but thats the point. If I wanted to repeal the 1st amendment and make a new one that makes it illegal to say anything against the government it could be "constitutional" but I would be still be a fringe nutjob
Using your rather twisted logic, if I, as a member of the Constitution Party, said that I wanted to scrap the 1st Amendment and substitute some other type of "free speech" kind of amendment or revision to it,
just how far do you actually think that would go? That's a rhetorical question, btw.
Answer: Nowhere. There are lots of people who want to do lots of different things, but that doesn't make them "fringe nutjobs" necessarily. As long as they're working within the framework of COTUS, let 'em have at it. They're pissing in the wind, frankly, but it's their right and duty to try and affect government the way they see fit.
If they can actually pull it off, of course.