I'm guessing that some standards will be updated to premiums (cockpits and all) but I doubt that they all will. It's too big a job to do. Saying that though I don't expect the Standards to be so bad looking in general as they are in GT5. They will have had probably updated them a little bit.
Ultimately no one knows but the people at PD. I wouldn't spend too much time thinking of GT6 if I were you. Just enjoy GT5 and GT6 will come out before you know it.