Is multiple routes possible like the original Outrun with varying difficulty? And then a combined consecutive super stage with all stages in a row.
Also, I don't think you should add drifting like Outrun 2/Coast to coast etc it made the game too easy as you car was almost invincible while drifting to collisions with other cars. Original Outrun handling was just pure brilliant arcade game play, hard, challenging but fair with no gimmicks.
Something else I remember is that that Turbo Outrun had a much lower view than the original Outrun. It was too low and your own car would block the view of the road and traffic ahead, very annoying. If anyone played Top Speed/Full throttle you will also know what I mean as it suffers the same thing. Thankfully Taito raised the view up for Chase HQ.
Congratulations on your game, it's really enjoyable and sticks to it's 80s Outrun roots.