As of Update 7, they seem to not add any Recently added to Motorsport spotlight cars in the Featured Career Mode on that update. They seem to be focused on cars that are already in the game like the ones since launch.
For example:
Spotlight Cars for Update 7:
1981 Ford #2 Zakspeed Racing Capri Turbo (car added since launch)
1969 Lola #6 Sunoco T70 MkIIIB (car added since launch)
1967 Brabham BT24 (car added since launch)
1988 Jaguar #1 Jaguar Racing XJR-9 (car added since launch)
Reward Car: 1977 Renault #15 Equipe Renault Elf R.S. 01 (which is a recently added car)
Spotlight Cars for future updates:
Recently added car
Recently added car
Recently added car
Recently added car
Reward Car: Recently added car
What I mean by Recently added to Motorsport, are the ones that are not in the new Forza Motorsport such as New to Motorsport & Returning to Motorsport