Speaking as a distant observer, I see it as somewhat odd that the government gets involved with party candidate selection; surely this is the job of the parties themselves. It is certainly strange to push this into the hands of the Federal Government, rather than the several states.
On the other hand, I state clearly that if the states themselves decide for reasons of their own decide to move their primaries to a single date, they can do so. And if 2/3rds of the states do that, the result will be achieved. A few states not in the agreement will not sabotage the plan.
John / Billybob