I'm sure Forza 6 will be the game that Forza 5 had to be. Forza 5 was made in a rush to have a launch title (which wasn't bad but not good compared to the earlier Forza games). However, Forza 6 will be what everyone expected from 5, I guess.
Just look how cool Horizon 2 was and now a Forza Motorsport with the same features (except open world), more cars and of course stable 60 FPS @ 1080p.
Did I say I'm sure it will be great?
Yes, I loved Forza 2, 3, 4 and was disappointed by 5, but 6 will be great again.