My Theory (concerning the campaign)

[Mendicant_Bias]

I believe that the Forerunner construct we saw in the desert in the Halo 5 reveal trailer is either controlled by, or is in fact, Mendicant Bias.

I believe Mendicant Bias is using Master Chief to bring back the Didact/UrDidact from the Domain in an effort to stop the Precursors, and is possibly leading Master Chief to believe that he can bring back Cortana through the Domain, whether or not it's actually true.
 

I believe the Didact/UrDidact conscouisness was copied onto the Domain prior to being corrupted by the Gravemind, and that Mendicant Bias is trying to further redeem himself by doing everything in his power to stop the Precursors and preserve the Mantle.

I believe that at some point in Halo 5's campaign, Locke, the Didact/UrDidact, Master Chief, the Arbiter, and others will band together to stop the Precursors, and this will culminate in Halo 6.

[Drizzy_Dan]

What evidence do you have to back up this theory? I don't believe we'll be seeing Precursors in Halo 5 just yet (maybe in the Legendary ending?). There's still much more going on that has yet to be resolved. We were also told that the Halo Xbox One E3 2013 teaser was not canonical to Halo 5 but was more of a representation of what 343 has planned for Chief's future in general: http://gamerant.com/halo-e3-trailer-not-halo-5/

[haloman 2]

@Drizzy_Deathbringer

even thoug that trailer wasnt a halo "5" trailer it still was in a kind of way because when it has the halo text in the clouds

if you look at the top right corner you can see a "5" in the clouds, a lot like what bungie did with "destiny" in one of the custscenes of halo 3

 

 

at 1:57 you can see a 5 behind halo

 

 

anyways my opinion is they will hint at previous halo games and the precursers as well as the flood

i really want to see the flood reappear

[DIABLO 0166]

It is possible that master chief may live or he might fake his death.

[haloman 2]

i would like the idea where he "dies" and everyone thinks he is dead including his friends (like where he technically does die but survives it just looked like he died and he got seriously hurt, like in avatar the last airbender at the end of season 2)

 

and he meets some new aliens or old covenant aliens who have no affiliation with either side but just want to help him and he makes new friends and then saves blue team (like they were captured or something or just about to die) and cheif comes back with an army of aliens and saves his friends with the arbiter and counter attack their enemies, whether its fire team osiris or the covenant faction and promethians