It appears as though Air France-KLM Flying Blue and Singapore Airlines Krisflyer are new American Express Membership Rewards transfer partners.

They show up on the list, anyway, though when clicking for more details you get

The reward you requested is currently unavailable.

So I imagine this is coming soon.

Good news indeed that American Express seems to be adding partners after losing so many over the past several years. Alas, Singapore is a Star Alliance carrier and there are already others in the program, and Air France KLM is Skyteam adding to that alliance’s already heavy representation. A oneworld partner would sure be nice!