I feel like the approach will probably be that railcards become digital wallet compatible.
costco already has this for ID cards in the states (and I've also seen it for account ID for home depot and some other places where it's tied to discounts). the app will pull up an ID card with a QR code that changes every 60 seconds or so to prevent screenshotting and trivial reuse, which is analogous to the function the chip performs in terms of challenge-authentication.
You’d have to have a national railcard first. The only railcards that exist are specific ones for specific groups.
National Railcard is the name that TfL uses to refer to all of those different types of card.