This would make no sense -- it would destroy the value prop of the AMEX Plat (because you already face Centurion restrictions and literally every other AMEX Plat benefit is like a coupon book these days). AMEX didn't shell out all that money to Delta for them to turn around and kill the value of their premium cards.

Don't forget AMEX has started building Centurion Lounges in Delta hubs which is a nod to providing additional lounge space for AMEX members (ATL, JFK, DCA, plus expansions are coming for SFO and SEA)