It would be meaningless because the Union could be unraveled by any unpopular decision the government might make. It would once again place the government under the constraints of unanimity which was the reason the Articles became useless and the Constitutional Convention was called. Thus it is contradictory to the whole idea behind the CC and the Constitution resulting therefore. Since restricting state power was the driving force behind the CC it would be absurd to place an amendment within the Constitution resurrecting that destructive power. Our Founders were not that stupid.
It is false that the 10th has ever been a check on the fedgov it and the 9th are just too vague and could have been left out of the document entirely with little effect. Hence my conclusion that they were just sops to anti-federalist agitation.
So it could, but the Union was a lot more resilient than you seem to give it credit for. For over 70 years the Union stayed together -- all the while the right to secede under the Tenth was there but not invoked. The Union weathered the first nullification crisis (SC and the tariff) in the 1830s but not the second (Northern personal liberty laws and equal rights to the territories) in the 1850s.
The Union did not cease simply because the South left. It certainly stayed intact and waged a major war.
You might run your view of the Ninth and Tenth Amendments as suckerbait for the rubes past Chief Justice Rehnquist, who (with J's Scalia and Thomas) has been very active in the rehabilitation of the Tenth Amendment and the limitations it places on assumptions (usurpations) of federal power. Particularly since, as I posted to you and you seem to be ignoring pretty obdurately, the Tenth Amendment was the one which in particular allowed the Constitution itself to be ratified -- the sine qua non, the one that gets Hamilton's eggs sent back if the Federalists don't come across.
At least you've told us something important about yourself -- that you believe in easy promises and welshing. Very Clintonoid of you.
Tell your interesting theory about the Tenth Amendment to Scalia and you'll wind up asking a proctologist to perform an emergency amendmentectomy.