Those who follow constitutional law scholarship closely, particularly as it pertains to the commerce power, will know that there has been a resurgence in interest over the past year in Resolution VI of the Virginia Plan -- the part of the Virginia proposal at the Constitutional Convention that would have given Congress the authority to legislate on all matters in which the states are "separately incompetent." It is hardly coincidental that this matter has become academically fashionable just as the ACA heads to the Supreme Court.
There is an interesting conversation ongoing over at the Volokh Conspiracy about the topic, which I highly recommend:
* Here is a post by Ilya Somin.
* Here is one from Neil Siegel.
* And here is one from Kurt Lash.