Agreed. My point is that I think that a state officeholder would have an almost insurmountable advantage over the common man when running for convention delegate. On the other hand, there would be more state delegates than the state legislature could tolerate losing for the duration, so others would have to participate. I would still be suspicious of "ringers."
Technically, an amendment altering the Supremacy Clause might be possible because Article V doesn't forbid it.
I'm asking about Article VI implications.
If you reread Article VI Section 2, I think that actually does forbid amending the supremacy of the Constitution ("... any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.") To me, this means that you cannot amend the Constitution so that the Constitution is no longer the supreme law of the land, because that amendment would be a "thing in the Constitution" that would be in conflict with this section.
I'm not aware of any other language in the Constitution that makes such restrictions on what can be amended.
I think that phrase is best understood as meaning anything in the State constitutions.
For this particular point, you will be pleased to know that these laws usually forbid state legislators from running for these positions.
A fundamental premise of parliamentary government is that a parliament cannot bind a future parliament, so no matter how much you try to craft a document that purports to bind future parliaments (i.e., this part of the Constitution cannot be amended), the effort is simply non-binding on future parliaments.
This is interesting for a couple of reasons in our history. First, the Constitution explicitly states that the slavery issue cannot be amended until a future date--I think 1808, or something of the sort.
Second, in an effort to avert the impending civil war, a constitutional amendment was introduced in Congress (by an Ohio senator) that would have purportedly guaranteed--in perpetuity--that slavery would continue in the South. This was the Corwin Amendment, and if you read Lincoln's first inaugural address, he makes a passing reference to it. As I recall, it was ratified in a couple of Northern states, but before it really ever went anywhere the civil war started and the issue became moot.
But I think it is interesting that this amendment was supposed to have been unamendable, and it raises some novel issues. At the end of the day, though, I think the best response is that parliament can't bind future parliaments; thus, any "unamendable" stuff doesn't hold water