you should go check out halo: forward unto dawn
its a webseries, thats 3 episodes in about halo. the production value is (imo) better than the Halo ad. and its a full web series, with 15 min per episode
Last I heard its in production hell because they needed several studios to cover its budget and they couldn't get along or thought it was too ambitious. Who knows.
I can see it happening. I mean if the Gears of War movie has started up again, then Halo can certainly do the same.