FreeGameDev

I had a great time playing against Alyan, theTomasPat, nobi and others today and this is how it started:
I went to Strasbourg Custom 2 and started racing just by myself, so that people would see that somebody is on that server. It took like 3 races for others to start joining in and then we had a total blast, at least I did.
When you let people race on your server by themselves, they have something to do while waiting others to join. I think that's the way to help people meet to play STK online.

Yes, often people will check servers but not go in if there is nobody else. But once you go into a server, you will often have someone joining in the next fifteen minutes.

I still cant's figure out quite what you mean by single race

They just mean racing by yourself—that way you don't have to wait in the lobby for other racers, you can do "practice" rounds in the meantime. I think it's a good idea unless there's some complication I don't know about. It probably won't really be necessary when 0.10.0 is officially released though and empty rooms become less common. Hopefully.

It could be implemented in such a way that any empty slots in the game setup will be filled by AIs. This would also allow mixed human/AI races with more than 1 human player.

The AI in networking is dumb, and there is no plan to change it as we wouldn't want a player using an AI to race for him.