This seems like complete make believe.
Sony has staunchly come out against cross play so the potential biggest game of 2018, that Sony has marketing rights with, is going to be the company that forces Sony's hand on the issue? Yeah right.
One of the biggest pluses of cross play would be that it extends the life of a game's online service by breaking down barriers and putting all players in the same pool. That's something RDR2 will never struggle with. I don't get why they'd even care or what benefit it would bring them.