The "Spend $50 or more, get $50 back" on inKind (payment app to which you add credit that can be used in some restaurants in some cities) is still around. I had it on my old vanilla Platinum in December and my wife's new MS Platinum has it now. However, it seems like you can't add $50 credit to the app any more (as you could when I originally used it); the lowest amount appears to be $95.

If you don't have enough credit in your account it seems like it just charges the default card in the account. So, if I added my wife's card to my account (but didn't deposit anything) and went to pay a bill with the ~$8 I have left in there from my original top-up, I think it should just charge her card for anything over the $8—and I would think that would work just as well from Amex's perspective as adding credit.