Except the authoritative finding would have to be judicial - any state that kept him off the ballot on those grounds would be subjected to a lawsuit that would end up in the Supreme Court. https://twitter.com/londonvinjamuri/status/1348905868037861376

And it's not clear SCOTUS would hold that Trump's statements constituted "insurrection or rebellion," or would want to do so.

(Trump's statements are not clear enough to be interpretable as a crime, and adjudicating them absent criminal charges is the -last- thing Roberts would want to be doing, and with reason.)

(This provision notably was very haphazardly enforced wrt actual Confederates, to whom it was originally supposed to apply.)

In general, attempts to get around impeachment are bound to fail because impeachment is the constitutionally provided remedy.

It's a nifty idea, though