I'm not super excited about this because it's kind of limited, but I'm not sure how much further we could go for wagneers without introducing a LOT more complexity.
I will say that I think that while "required" may be a quality of the left card (eg the company in this example), other validations are likely to be properties of the plus card. Eg, let's say that a company requires a valid email. The requirement itself is a quality of the company card. The validity of the email is a quality of the email card.
(Stream of consciousness). You could make the case that this could be just one setting, like "*valid". Structured cards would work as describe above. Other cards could have lists of optional validations appropriate to their type / set. Hmm.
Current leaning: change *required to *require (more consistent with verbs for permission validations and would work with this proposal).