Going by the explanation given by Mr Beard Guy, the main difference between patch optimized and built for xsx optimized is that patch is for already released game, built for will be for games after/at the release of the console (there by not needing a patch).
It just means it was compiled on the xsx dev kit.
So it doesn't have to mean anything you've said at all.
Your pretty much talking two different builds of the game. Not gonna happen this cross gen, for either console.
Be a huge waste of development time and money, better spent on assets or bigger levels etc
So if they mean "native" as in not backwards compatibility mode, the renderer and the engine subsystems will still be different on the Series X because it has different hardware with different capabilities. It will be two different code paths and effectively work as I stated.