I would like it if there's a Cars 3, as well as if it's released in the same year as a sequel to the film Rio. I actually do like Tailsyochicken's idea, but here's one from me.
It might have humans coming across into the Cars universe and notice the stuff there, as well as bringing some non-talking cars. They might enjoy the sights of the places in the Cars world. And the characters might be wondering what the stuff in the human world looks like, so they might come along to the human universe, and have races in these places, but some human and car villains come along and try to sabotage the races, and even prevent Lightning McQueen from winning the races, so McQueen, Mater, Finn McMissile and Holley Shiftwell must come up with a plan to stop them.