It will be apart of their contract with Sony that they can't discuss the x version. They might be able too after launch but deffo not before. Think how many people would buy an x for this game if they knew it was considerably better.
Sony pay to get their name slapped on adverts and bundles leading up to and after launch. Honestly too much is read into these marketing deals.
Rockstar will utilise both consoles to the max, it's what they've always done, and if the X ends up being the superior version then the impact that has for Sony and Rockstar is minimal.
Any people buying an X for the improvements is going to be weighed out by those picking the PS version because they saw it advertised with Sony's marketing attached.
The only L Sony will take is going to be in the faceoff category and at this stage of this gen those hardly carry the weight they did five years ago.