Kaz has mentioned online quite a lot without giving too many details but I would like to think they are going to do it proper. The GTP online was shocking, I gave up trying to get connected half the time.
I think that if this is not in PD will have a big problem. Not for me because i will play off and online. But most people i know are only buying when we can create private rooms. Because this is where you have control over people that f. up. With far over 40 friends we can always get a race full.
Private lobbies was also apparently in the feature list they posted on Polyphony Digital's official site (in Japanese) during TGS last year, then removed a few hours later. I'd be totally shocked if there was no way to group up with some friends for private racing, that would be epic fail.