Private hosted rooms are a good idea, in essence. Although there will be some expenses towards servers, chances are that there will be more profit for diamond rank as is it a pivot rank (Pretty much voting and then these private hosted rooms). Not only this, the basic idea of it all is quite simple, and somewhat easier to code than the party system. The thing is with the party system, if a game is full, and you join, not everyone will join, then you have to go through this whole system of a rendezvous point, and such. A private hosted room is pretty simple. Invite someone, start a game and play it. Yes, people might think that a party system is more useful in some way, which I agree, however I think what
@SamueLogic is trying to do is to encourage donations. Donations -> More Development -> More games for people to enjoy. This, all in all, is a very good idea. With little tweaks, here and there, to provide the "CubeCraft Unique Touch-Thing" (Yes, I just made that up), it will definitely promote donations.
An idea that I had was that the room could have different game-types that you wouldn't see in the actual server, like different small minigames, like 1v1s, and stuff like that.