AX and CO have a strong relationship and the CO membership has come to expect the benefits provided by this.
If MR were to pull the plug on being able to pump points over to CO, I suspect we'd see a notable reaction from any level of cardholder (and I suspect AX knows this too.)
W/r/t to lounge access -- I'm not sure a Green/Gold member would care, but if Plats loose lounge access to the successor of UA+CO, then I'd think AX would a) loose their CO flyers who previously held the card for lounge access and b) have to offer to discount the yearly fee or add additional benefits to compensate for the loss.