How can it not require permission from the parties as to how they pick their party’s nominees? Unless you mean just put any candidate who is “serious” according to some criterion on the ballot and ignore any party endorsement, but (a) what criterion would you choose? The same ones used by the networks to decide who got to debate? and (b) doesn’t this just effectively turn the national primary into the first step of a 2-step general election, with the party primaries determining which of their candidates is the one that isn’t required by the party to decline to participate in the national primary?