My Reclaimer Trilogy theories are these:
1. Line instalation:
- The planet that the remains of Forward Unto Dawn are heading to is a line instalation, it shot the Dawn (this would explain why it was on fire again on the trailer)
- Since is a Flood research facility, there must be flood, and there has to be something to test the Flood with (any species that can be infected).
- Humans, or Covenat species may be stuck in the planet because they were shot down, and the forerunner constructs are testing the Flood on them.
- If there are Humans or other species on the planet, they may have weapons and vehicles on the crashed ships.
- John, along with the other Humans and any other "smart enough" Covenant soldiers try to escape.
- On the surface they find new creatures that the constructs have not been able to deal with, causing a fight and many casualties in a 3 way battle.
2. Flood dust:
- The first time that living creatures made contact with the Flood, was on a vast planet, and the Flood was... Powder.
- The ship that crashed on Instalation 04 can be one of those vessels that contain this Flood powder.
3. Instalation 00:
- The Ark could be repaired by Constructors, they still had a giant moon for resources.
- Instalation 04C is built. This instalation has no Flood lifeform.
- Instalation 05 was also sterilized by the Elites, this means there are no flood here.
- The other instalations still contain flood. This could indicate John will probably visit other rings.
- According to the books, there is a Precursor on the galaxy, if it survived the Halo firing, it may be hidden.
- Medicant Bias said he had a new master. Could be talking about this Precursor, or the Gravemind.
- The Precursors were Tier 0, if The Timeless One knew about the technology he had at hand, it could do anything.
- If the Forerunners were able to keep the species alive by storing their DNA and building the creatures again, they were able to do the same with their own species.
- The had Shield Worlds, these were away from the Halo range.
6. Shield World:
- The planet could be a shield world. I don´t think it´s Onyx because it exploded.
- Humanity gets the beacon that Cortana was sending, and go to search John.
- Or Elites get the beacon instead, and for honor and knowing they were allied with the Humans once, Thel orders to go to search John.
8. Angry Brutes:
- The Brutes attack Sanghelios.
- Someone discovers the Forerunner technology to mutate almost instantly, and uses this technology to mutate any creature for specific tasks.
I can´t think about anything else...
BTW, according to the word "Haven" written at the end of one of the termianls in Forerunner text indicates that it may be a Shield World.