I think we need 5 ten state primary dates.
On each date we could have 2 states from the north, south, east, west and central. States from each region would be chosen by lottery.
More Super Tuesday-type days will mean any serious candidate will need tens of millions of dollars before primaries start. Are we sure we want that?
Just one problem with that: the cost of a ten-state primary.
A schedule like that will run every candidate who hasn't lined up a group of deep pockets out of the running. It's a near guarantee that the establishment wins 80-90% of the time.
The benefit of one-state-at-a-time at the outset is that it allows underfunded candidates to make their case, conceivably win...and start picking up donors.