I hope it's not BTCC because that just wont add much to the game. The cars are virtually the same and we already have a mod for it. The tracks are also around as addons but I guess they aren't great quality.
It has already been mentioned in previews that Race Pro will get DLC that will contain some historic racing cars, kinda like GTL I guess. Maybe we'll be getting them too? After all, Race Pro shares most of the content with GTR Evo. And they would be getting more money out of the same artwork.
But since we already have the GTL conversion that might not happen either.
A1 maybe? Who knows, but I look forward to finding out.
Anyway, thanks for the hint Simbin.
Edit: One thing I would like to add,
a message to Simbin - Please get rid of or increase the ModelID limit for cars. It's the one great barrier for modding that the game has right now.
Look here for info on it:
http://www.nogripracing.com/forum/showthread.php?t=34808
Right now it can't go higher than 255, and the limit is quickly being approached.
Just hoping Simbin reads this