I think it should be up to the clubs to decide what way they want to issue tickets for games. The clubs are more in touch with what format their fans would prefer to have to gain access to games. I still prefer to have a physical ticket in my hand, whether a paper ticket or card, when I go to a game. Digital ticketing sounds great until your phone packs in and you can`t get access to the ticket. I`ve gone to matches for years and when you had a paper ticket or season card all you had to do is not lose it before getting to the gate.
The switch to using plastic cards was probably more of an attempt to stop ticket touting, as it made it harder to sell your season ticket for individual games as you couldn`t hand you card to anybody as you`d need to get it back for the next game. But folks have found ways around this, so I think going digital is more a way to clamp down on folks selling tickets themselves for a bit of a premium.