They will all get updated at some point, we just don't know when. All that has been heard is that the GTRX, GTR1, and GTR2 classes will be reorganized into a kind of gte spec class (I'm not too fond of this idea), and that the Pagani will get its own cup class. S3 has been rather busy with new content and hasn't had the time to look back at some of the older stuff.
Would be nice if GTR2 is updated. They are not as good to drive as the newer cars while GT2 is one of my favorite class.