The Terminals are the only ones confirmed.
But I’m hoping for the following easter eggs:
Jonesy (the cat from the “wanted” posters on PoA) to make a cameo. If you can find him that is. Maybe like the monkey-men on H3.
[Gravity Rifle.](Gravity Rifle | Halo Alpha | Fandom) Acting much like the Scarab Gun in H2. The original model is already in the source code, so 343i can easily use this concept and make a cool easter egg from it. Place it somewhere hard to reach.
Zuka 'Zanamee making an actual cameo this time. He was the Spec Ops Elite from The Flood who was hunting down Chief on Halo. He is also the Elite in the elevator that comes down after you destroyed the PoA’s engines in The Maw, but he doesn’t match the description of the book. So I’m hoping he will this time actually be in.
Engineers. Already in the source code. Give them a non-combat “purpose” like hints as to where we can find Terminals or whatever.