Haven’t seen a thread on this, so I’ll just guess that I’m the first one to post this here.
Yes, Social Playlists are coming. 343 are working on it at the very least.
Josh Holmes replied to a user on Team Beyond who complained about the lack of Social Playlists in the game and this was his response.
> There was no insidious motivation behind going all ranked for Arena. That was the design intent of the team working on that experience. That said, we’ve heard the requests and we are actively working towards supporting unranked playlists for Arena in a future update. It may seem straightforward on the surface but lighting up unranked play in Arena is not as simple as flipping a switch.
>
> TLDR; We hear you, and are working on it.
Here’s a link to the actual post on Team Beyond: http://teambeyond.net/forum/topic/5443-halo-5-guardians-discussion/page-3234#entry613139