Long story short: Starting with Wilds of Eldraine, duplicate protection for rare and mythic rare "reprints" (existing cards reappearing in a newer set) will apply regardless of the artwork; if you have four copies of a card in your collection, any additional versions will be duplicate protected as a reprint.
This is MASSIVE. I have hated the current system of accumulating duplicate rares every time wizards decides to reprint a rare, especially lands.