This is something that I really like about certain games, and I am that kind of guy that don't really want hundreds of people around doing the same thing as me but I do get by in MMOs. I'd rather group together with a bunch of friends in a world where we are the only ones. I played on a private server for WoW with my friends and siblings once and it felt very refreshing to me as well as for them to not worry about other players, do things at our own pace and just have a really great adventure only the five of us.
So my question is, would you like to see the option to rent private instances that only people that you invite can enter?