Interestingly online payments with Maestro (what cards are commonly co-branded with right now) are possible as well with quite a few sites, but the Maestro card number is not exposed and even if you manage to get it, I believe the cards are typically not enabled for that.

That's a peculiar choice, but I assume the decision was made to appeal to the typically skeptical German market. I do wonder why it wasn't made opt-in, though.