The original Black card - now labelled Legacy Black attracted higher cash back. That plus a nice wallet cost at the time £50. Those cash-back benefits remain. But there’ll be no further extension of benefits for those who remain with that card. Effectively in a cul-de-sac.
There’s a new Black card. That will attract new benefits packages (which are yet to clarified) but will be subject to subscription.
The Blue card remains with lower cash-back but it WILL benefit from some future benefits (such as Apple Pay and Google-Pay which are currently being explored). Not a subscription service.
A two-tier service with a third (Legacy) effectively parked.