In my opinion there are a few options for discovering who the next antagonist will be and who won't.
First the didact, his parameters are uncertain, his symbol appears in the halo 4 E3 trailer, but now it's upside down and turned red instead of light blue, just as mendicant bias symbol changed color after going rampant, now, we don't really know if he will be the next antagonist or not, but if he is, I beleive there is a posibility that in some point in time he used the conformer process to transfer his mind and consciousness to some type of artficial vehicle enabling him to further his life span, maybe the black-orange sphere in the E3 trailer is being controlled by the didact, why he doesn't attack master chief remains a mystery (you could fill in the gap here), but you can see that the light scanning master chief is the exact same light that scans the infinity and also when the infinity is being scanned you can see the rampant didact symbol. Or he isn't the antagonist but rather he is in combat mode just as penitent tangent from delta halo in halo 2 and is on a mission but needs RECLAIMER help, this is from the aurora cygnus site:
Welcome, I was about to fire upon you then i realized who you are, we have been seeking you and "HE" is looking for answers for what happened, but be cautious with him and tread carefully.
If you explore the site carefully you can clearly see that aurora cygnus is communicating with cortana.
Now to my next possible antagonist.
The contender class A.I. 05-032 Mendicant Bias. Now, we all know he wen't rampant and attacked his "makers" but was then defeated and his compound mind broken into it's component sections wich were then scattered throughout the few remaining ships of offensive bias's fleet for transport. We now also that from the events regarding adjutant reflex and the i love bees site that mendicant has been recovering his component sections, this is also evident from the end of halo 2 where cortana fights an unknown but familiar A.I. (mendicant), and upon returning to earth and then to installation 00 were the last shard of mendicant´s compound mind was installed, he was finally complete again, the problem here is that he now tries to help master chief by seeking atonement and stating that he would help master chief, but we don't know for sure what happened afterwards, so think, maybe by being complete again he could have re-entered rampancy, and begin a new attack plan but know against forerunners and reclaimers, now check this, this is from the aurora cygnus artifact site:
>/[0-575-07716-6]
It has deceived you for too long, it has deceived my makers for too long.
I was the one they trusted, I was the one that saved their lives countless times.
It turned them against me, how could they have not have seen the truth.
This so called devoted construct has taken what I should have earned, claimed what I had shaped.
The damage is too great for it to be swept aside.
I now have something that the construct failed to protect, and they will know for what they had should have known.
To me it sounds like mendicant's revenge for being defeated, and on the http://artifact.at.ua/ site you can clearly see that aurora cygnus is trying to deflect an attack from a known foe:
>/[DATA ANALYSIS COMPLETE].
Not good, not good at all, it appears it has reestablished a conscious state.
>/[sENDING RECOVERED TRANSMISSION TO 502-XRT]...
>/[APPROXIMATELY 13 HOURS FOR TRANSMISSION TO ARRIVE].
>/[ERROR CODE: ///]
>/[TRANSMISSION FAILED TO REACH DESTINATION 502-XRT]
>/[sEARCHING OTHER AVAILABLE INLETS]...
>/[sEARCH COMPLETE/: 1 INLET AVAILABLE/: 505-XRT INLET AVAILABLE]
>/[DIVERTING TRANSMISSION TO 505-XRT]
>/[ERROR CODE: ///]
>/[TRANSMISSION FAILED TO DIVERT]
It's preventing them from knowing it's conscious.
Now from what I see aurora cygnus knew "IT" was once conscious, then it wasn't, and then it regained it's conciousness. Who else but a broken compound mind put together again.
My 3rd and final antagonist would be ....... Cortana
And I base this opinion again on the aurora cygnus site, at first you can see that A.C recognizes cortana as a friend, but suddenly a virus starts an attack on the conventus facility (requiem planet in my opinion), forcing A.C to leave, but the thing is we never get a response from cortana, all we get is the attack from this unknown entity, which ultimately takes over the facility, now remembering the halo 3 ending, the first half of the forward until dawn wich contained the arbiter makes it through the portal and out, but the part where the chief is, doesn't quite make it out and is sent to an unkown location leading to requiem, coincidence? I think not, due to cortana's previous blind jumps into slipspace in which she always manages to come across some new discovery, I believe Cortana makes the arrangements to arrive at requiem, but in order to do this she has to be looking for something, what that something is I don't know.
But if anyone takes the time to read this post and feels like filling in the gaps as well as spoting any possible error on my facts, agrees or disagrees with anything written here please feel free to comment, thank you for you're time.
Oh and sorry for bad grammar, I'm actually mexican and not used to the language.
