I agree that no one knows what the new "merged" program will look like nor what it will take to get LT status (assuming they still have one of course.) But if they continue to have one, I would guess the most likely scenario is that they will merge the nights from both programs. Which if they do that, then staying with Starwood for now would still help you in your future drive to LT status.

And you could still enjoy all the benefits you've achieved with your current SPG Plat status.