To improve Curve’s “All your cards in one” idea, I would love to see that the Curve card becomes a dual scheme card. MasterCard&Maestro (probably easiest to implement) or Visa&V PAY (probably more difficult to implement).
This idea will increase the acceptance of the Curve card at merchants in countries as the Netherlands, Belgium, Germany, Austria (and more?). And will not lead to any loss of acceptance in any other country.
The advantage of a dual scheme card versus two separate Curve cards (e.g. a separate Maestro one and a separate MasterCard one) is that you only need to carry one card (“All your cards in one”).