Ever since Reach, I’ve loved the idea of being able to play the campaign in your style of armor. Of course, canonically, you can’t do this in other campaigns because you play as Master Chief and he has a specific look. However, if there was a skull introduced that gave you the option to do so, then there doesn’t need to be a canon reason to be able to do it.
343 seems like they are going to be spending a lot of their focus on cosmetics due to the Battle Passes, so I feel a skull like this would make sense so players can get as much play out of their armor as they want. Cutscenes also look like they are rendered in-engine, so it could be a great way to show off your style in the Zeta Halo environment as well.
And once co-op is added, it could allow your friends to be more visible as well, instead of a Master Chief clone or a generic Spartan or whatever their plan is for the co-op players. Also as a side note, it would be great if your co-op buddy would appear in cutscenes as well, even if they are standing at the back of the room or just enough out of the way. Halo CE made the small effort to have 2 Chiefs step out of the cryo-pod at the start of the game, and I personally appreciate if their was more effort to include your buddy in the story moments for those that care about those little details.