The first state should be the one with the closest margin from the previous election.
Out of curiosity, here's how this system of determining the first primary state would have played out:
2024: Georgia
2020: Michigan
2016: Florida
2012: Missouri
2008: Wisconsin
2004: Florida
2000: Kentucky
1996: Georgia
1992: Washington
1988: Minnesota
1984: Massachusetts
1980: Oregon
1976: Minnesota
1972: Missouri
1968: Arizona
1964: Hawaii
It's not the worst way of deciding who goes first, even if it's still a bit of an arbitrary reason.