With such a great collection of cars and the idea behind the game being to get to know the car your racing it would be a fantastic idea to have historic themed cups.
The cup would effectively tell you the history of the car and get you to race it in its original form, then after perhaps a few or even one race move to a newer car of that same manufacturer and learn about it and race it. Naturally all car models could not be incorporated for some but a reasonably in depth overview would be great.
Many examples could be given however we could have the Mazda Cosmo with their first rotary, then an RX3 then RX7 and finishing off with an RX8.
This can also be done with manufacturers showing their progress through the decades starting with their first or early model and progressing to the latest.
The idea behind this is to learn more about the cars or manufacturers. The story would need to be more involved than some of those in Forza Horizon and would need to be more progressive.
Would be a fantastic addition. Naturally racing on historic tracks for that era of car wpuld be even more awesome!