The thing people keep missing here is that Gorsuch said yes states do have a role in keeping ineligible people off the ballot, BUT it is a giant open question as to whether Trump is actually ineligible.
Arguably the 14th amendment claim doesn't hold.
So when the article says he's 90% of the way, or whatever, it's overlooking that that question is unresolved and is itself 90% of what we're talking about here.
Yes the state can absolutely boot an ineligible person from the ballot, but there's enormous argument over whether or not Trump is actually ineligible.