Update:
Although the preview of "Till the World Ends" that surfaced on Amazon UK sounds distinctly like Britney, Shoshanna Stone, who works as Britney's PR for Sony, just tweeted that clip floating around is NOT Britney's song. Here is her tweet below:
I ****ING LOVE IT!!!! I dun really care if is generic as long as is great pop dance music and it seems like is going to be. Trust, she will not dissapoint.