Some cars I'd love to see included in future DLC are as follows:
Early Mazda's such as Series 1 or 2 RX7, RX3, etc etc.
2008 Nissan GTR - It's an amazing car, would love to race it in Forza.
Toyota Gen 6 GT-Four Celica (ST-205) - My favourite car i've owned in real life to date.
Some utes, they would make an interesting challenge with their light back ends.
Some larger cars, like Subaru Forester for example.
Just more Japanesse cars, I love em ;)