Yeah, it would really be cool if it was online. But I doubt they will have enough time to implement it. It took the THPS3 team a whole year to get their online feature working -- but that was while working on the main game too.
If they did make it online, it shouldn\'t be too hard to make the customs maps usable. All they have to do is have all the players download the map from the host and save it onto their memory cards (or maybe even HDDs).