No one can give you a definite answer at this moment, even the devs, I guess. S2 still needs time to be finalize, I am sure the devs are working on some of the S3 content, as adding a new car or track cannot be done by a week or two.
Well, no one knows the future. Maybe the DP1 in the suggestion forum will be added to S3, who knows? IMO, I'm just still new to this game thro, I still please what I own right now, got tons of cars and configurations to be try out in the future.
Personally, I would like to have another open-wheel car, coz I love them