I honestly hope they do. Some people will be like "Oh they already made an anniversary, its a waste to make another." But with the extreme advances of graphics from then and now, they really ought to, at least for Halo 2's own 10 year anniversary, if not Halo's in general 20th.
Terminals. All the different kinds of Elites in the game. The SPAAAAAACE BATTLES. The ODSTs coming down (they could include). Different CAMERA ANGLES in clipscenes. Re used weapon skins from previous Halo titles! Re used Vehicle skins that make absolutely no sense canically wise!