People are asking for an option to make activities solo that are not solo already, like strikes, easier nightfalls etc. That's what optional matchmaking means. It does not hurt squadplayers, as there would be a switch or something on mission start screen. Off - go solo. On - go with a random squad. In case you're with a friend, off - go with him only; on - rest of the squad would be randoms. Simple concept, apparently complicated to implement.