The only real argument I've seen against optional high-level matchmaking has been that teams would constantly fail and waste the development time it takes. Regardless of how much horseshit that may be, there's no denying that most nightfall attempts would be successful. It's just strikes that everybody has done a million times, just with some modifers. There's no real need for communication most of the time, so there's no real reason to not have matchmaking for it. Nightfalls would be a good step towards adding matchmaking to everything else.