They did add it, its called guided games. Failed miserably.

Guided games are not matchmaking, guides games are their idea of a sherpa, and the wait time is inexcusable Why would optional matchmaking be an issue if you want to use it ..go, if you have your team already established its a non issue, wheres the problem beyond your own personal preference For a "social co op" game, bungie puts way too many speedbumps in front of the social aspect

I don’t see them adding optional mm. Bungie will either make it always mm or leave how it is. They have never been good at giving people options.