Yes I don't think Amtrak will move to Grand Central. I think they should move to the New Penn Station. Just leave the Long Island Rail Road for MSG.
I take Amtrak sometimes and the ceiling in that tunnel is just horrible looking. It is the worst Amtrak platforms on a big city that I have seen.
Please this is NYC they should concider again to create a new platform on a new location as in the new Penn Station..