Sounds like there's a Hot Wheels movie ahead of us! Legendary Pictures (a close partner of Warner Bros) is indeed in negotiations to buy the film rights to Mattel's Hot Wheels, the popular die-cast model vehicles. According to Variety the live-action movie adaptation wouldn't target kids but a larger public: the plan is actually to somehow emulate the Fast and Furious craze. There's no director attached to the project yet, not even a scriptwriter.
Here's a 1968 commercial for Hot Wheels:
"A movie based on Hot Wheels, the popular die-cast model cars by Mattel. It will not be a kid movie: the plan is to develop a edgy film that could compare to Fast and Furious."
I kind of understand why Legendary Pictures prefer to develop a movie on an existing toy property than to create a brand new concept: it's an easier sell and investors feel like it's less risky. But they'd better come up with a good story and avoid to over-rely on CGI effects: they should keep in mind that the Speed Racer movie performed poorly even if it was based on a solid property...
Anyway, more information about the Hot Wheels movie as soon as details emerge.