To explain mkw, the host does not need to invite people in it - in fact he CAN'T. When you host a room in mkwii everyone on your friend roster will know as a purple smiley will start blinking on his friend roster (and inside the friend roster on you) and he can join in. Even people on your friend roster who are in a public game will be able to see if any friends are playing in either another public game (yellow smiley) or private game (again purple smiley) by the end of each race and choose to go to the friend roster to join said friend.
You could also instantly add anyone who's in a friend's private room at the same time as you... Or not completely accurate. You can only do it while you're in the lobby before the game starts. Appearntly the conduit will let you do this even without being in a game with them by just directly accessing your friends friend roster and pick people you want added on it

It was definetly operated pretty well, so if the conduit works like this then it will certainly be pretty good. Possibly better than MoH at least once you have added friends (even if there isn't a lobby where you can choose games to join in this).
Edit: One small negative thing about mkw was that you could only join private games through the host, so if a friend was in a private game, and you didn't have the hosts FC, you wouldn't be able to join.