Yep. This could get interesting. I love my Amex Platinum but if this happens I'd have to reconsider the card. I certainly get value out of it, but the relative cost of an AC membership plays a large part of that.
Considering that I can give myself an AC membership for free through BE, I'm not sure I'd keep my Plat and I certainly wouldn't give Citi the money without the rest of the benefits I'd expect for $450.