So what about the rear roof spoiler and rear spoilers for most of these car. Are forza going to make them for for all 3, 4, 5, and horizon 1,2?.

What we have now is what we get, for current and legacy Forza titles.

Are they going to make them for past titles?

Well, past titles have already been released and no new content is coming to them so it all depends on the vehicle. The Forza Adjustable Aero is available for all cars in Forza Motorsport 3, 4, and 5 and Forza Horizon 1 and 2.