I'm definitely keen to help out, here are some fan art renders Ive done so far of a title and one vehiclehttps://vimeo.com/158422744https://vimeo.com/162639394https://vimeo.com/163344222
I think it could be done without taking up too much of the devs time to help us. I think if there is either a build with a free camera or even easier for them just an orbiting camera around any car (cycle through the cars) as part of the replay system.
Though I dont know when they are planning to add a replay system. It would way to do the race part of the film as you could first drive the race from a normal view and cause whatever action to occur (example two particular cars are bitter rivals and you target them then wait until they attack you back etc) then you can go back and do dynamic angles of the action in the replay.
For the live action / CG dialogue shots, thats cool you have a chroma green. So you just need to find some actors in your area (which is where?) to act on the screen. You could even have a bright green/blue box they lean on like they are leaning against the step to their rollcage (I mean grip vehicle :p)
Then Id be happy to help composite this into a 3D scene using cinema 4D, its fairly easy to get a landscape happening that looks like it would be at one of the tracks, really basic but just defocus it so the focus is on the characters and cars.
For the cars Chris has already given me a Dominator 3D model compatible with Cinema 4D or Element. If we ask nice we might be able to get another 1 or 2. They are nicely detailed models so they can be big and close.