I hope Dusty has a cameo.
Its unlikely that they would write in his character to be part of the main story. But it would be a cool thing to have him cameo in a scene. Maybe something where Lightning is gearing up for a race somewhere, and happens to encounter Dusty as he's passing through or attending a fire safety course.
I love the Planes movies. I hope' they're making a third, but this will do until then.