It's coming! 19th of June. A recent Destiny Reddit leak post that's retroactively drawn attention due to repeatedly having made correct calls, claims that there will be an in-game Destiny event to "celebrate Bungie". They also claim that Bungie want Halo-themed cosmetics featured here, but due to the way it's written and how IP works it's not that likely to actually happen.
What is likely to happen however (and the leak explicitly claims) is Marathon tie-ins. At the very least I wouldn't be surprised to see vaguely Security-Officer themed armor, and maybe some nice lore references. But who knows. Another MIDA weapon would be nice!