Actually, i just finished a conversation with my friend Hiroshi, who i woke up because i forgot it was 7am over there (tokyo). He claims that there is work being done on a 5th stage, and that takumi will race in a semi-pro street circut at some point. Also, he claims that the next area of focus is going to be Chiba, Kanagawa and finally tokyo.
Ryosuke mentions Kanagawa in ID1