The only problem I see with this plan is that state populations aren't static and you're going to have to move things around every so often.
The moving dates also present a real cost to states like IL that use the presidential primary for the general primary. County clerks would be forced to change the date of the general primary every four years and that impacts a host of other dates like petitions, challenges, etc. When IL moved up the date this year from 3rd Tue Mar to 1st Tue Feb it was with a number of concessions to the clerks to make them agreeable. I don't see how that happens if imposed from the national party.
