While such a standalone product has not surfaced, it is possible that Apple finally views Motion 4 and other components of the updated Final Cut Studio released last week as a sufficient replacement for Shake's features.
You will never see Motion credited as the compositor in a major motion picture like Shake was. No one uses Motion for high-end work like they did with Shake. I challenge anyone to find an article with someone crediting Motion for FX work the way Shake was credited on movies like LOTR. I can't even find an article crediting Motion on a low budget Hollywood film.