That older thread reminded me so im bringing the discussion back.
A Custom Games Playlist would have been perfect. I was expecting it to happen in Halo 4 at first before launch.
Should act if your party is set to open, it opens up to a join in progress list in Matchmaking that allows people to choose from a list of custom games that shows the Map title and gametype and how many players in the lobby.
Friends only and Invite only games will function as normal. Can’t be hard at all. Battlefield does something similar.