Future updates to the forthcoming Halo 4 may add clan and Theater Mode campaign support, among other things, according to the most recent post on The Halo Bulletin.
When asked in a Q&A session about the future availability of Theater Mode for both the shooter's campaign and Spartan Ops modes, Halo Waypoint's Jessica O'Shea said:
"Theater Mode in Campaign did not make the cut for launch for various reasons of scheduling, rendering issues and some significant engine changes. However, we are treating Title Updates very differently for Halo 4 and rather than simply using them as opportunities for simple big fixes, we are thinking of them as a way to sustain and grow features and options, so it is possible you could see Saved Films made available for Campaign (as well as some other significant features) at some time in the not-too-distant future, but that's yet to be determined."
Later on, O'Shea was asked about clans, to which she responded:
"As we mentioned before, we plan to continue consistent and meaningful sustainment updates to improve and enhance player experience. Social constructs are something we too have missed since Halo 2, and we're looking at interesting ways to improve those experiences in the not-too-distant future. I will be using that expression a lot. Get used to it."
The Q&A is pretty extensive on the whole, and goes into such topics as future map packs, split-screen support, the betrayal system, and more, so check it out if you have any outstanding questions about 343's first foray into the franchise.
Thanks, OXM UK.