Well I'm sure if they have a new game planned they are already working on it
i'm not sure if it will release by 2010 but having a new one before the end of 2011 sounds very likely
I'm pretty sure they will be making a new city, likely a next-gen remake of either vice city or san andreas with new characters
also its a wonder whether they will continue within the present time of go back to the 80s or 90s like they did with vice city and san andreas.
we shall see