Every place I have seen '100% digital only tickets' always has a back-up for those without smart phones. Our NFL and NHL teams only have season tickets and regular tickets by digital. No paper tickets. Unless..... you visit the offices at the stadiums in person, they will print out paper tickets. Same with Ticketmaster and other ticket vendors. They'll create and accept a printed ticket too.
Disney doesn't have to make a physical plastic card, but they have to make some way to print out a QR code or something. Or there will be lawsuits.
Plus, what if the cell/wifi goes down, you can't enter the park at all? If the internet goes down for a day, parks are all closed?