Davina is Klaus's and Hayley's Kid from the FutureShe bears a striking resemblance to Hayley, and she is a super-powered witch (just like Klaus's mother).
The reason Davina is so powerful is because she's not entirely humanThe way she dresses, her calling the Originals 'The Old Ones'...she's got faerie in her from some distant supernatural ancestor, which augments her abilities.
Davina has her own agendaThe reason she agreed to help Marcel shut down the witches in the Quarter is because there's a hidden reservoir of pure magical power in New Orleans after centuries of witches living there. She needs the witches out of the way so she can have unlimited access to it, and eventually become strong enough to take Marcel and every other vampire out. In the meantime, she also needs Marcel to take care of the Originals, as their presence is somehow affecting her full potential (as if she's not strong enough already).
The baby is going to be the world's first dhampir, and nature's last-ditch effort to end Klaus once and for allSince a werewolf-vampire-mortal hybrid would cause too much of an imbalance in nature, the child is going to be a proper daywalker, half-vampire and half-human, who is immune to that pesky 'kill an Original and every vampire who shares their bloodline dies' loophole. And hir destiny will be to kill Klaus.
The baby could be the AntichristHayley will find out what the ominous Latin from 1.03 will be, and will eventually decide that destiny can go screw itself, and to raise her baby with goodness. What may make the baby evil is the environment and/or trauma of being raised by Klaus and all that entails.
Davina will unlink Sophie and HayleyAllowing the Originals to kill her.
Hayley is an Original WerewolfThe show is called "The Originals" but may refer to more than just Klaus/Rebekah and Elijah. It may include Hayley who has a wolf mark on her back, and seems to have some wolf protectors.
The resurrection aspect of the Harvest is complete and utter BullSophie like her sister belives that if she completes the Harvest by killing Davina, then Monique will be brought back to life vis a via the rebirth part of the Harvest ritual. But anyone who has seen the last couple of seasons of VampireDiaries can attest you can't cheat nature, just ask ask Bonnie and Jeremy and their current situation. Any group that has no problem turning some poor innocent insane to teach the local priest a lesson. Is the kind of group that will use bullshit to sugar coat human sacrifice.
Marcel never planned on giving Jane-Anne a second chance.He was waiting for her to slip up so he would have the opportunity to kill someone who willingly offered her child up for sacrifice which Marcel doesn't care for.
It is the baby, not Hayley the hybrids would be sired to
Hayley's ultimate ancestor is FenrirWhich would explain why her werewolf line is so revered as to be considered royalty.
The 'baby' will eventually become twinsSo far, the hybrid baby is capable of healing and can already produce hybrids from its blood without the Doppelganger. Its existence has been described as 'nature's loophole', so nature will correct that by having Hayley carry twins. The diffusion of blood will render their hybrid-making abilities to minimal.
A grown-up version of the baby will show upShe'll probably be a Dark Messiah at best or the Big Bad of a Bad Future. One thing she won't be is a Daddy's Little Villain.
The wolf helping Hayley is one of her siblingsIn the family tree left for her, there are a few names above hers, all born around the same time as she was. They're her older siblings, and one of them has been watching over her since the series began.
Marcel called Mikael to New OrleansIt explains why Mikael didn't kill him.
The reason for the Harvest Festival is not only to preserve the witches' powerIt's to prevent Celeste from absorbing that power for herself. After she died, she told Elijah to bury her in their special place between two oak saplings. Unknown to him, those trees are hallowed to witches and are one of the primary sources of magic in New Orleans. By burying her there, Elijah unknowingly puts her at the nexus of that magic, and her soul begins to absorb it so that she can be strong enough to wipe out the Originals. The other witches begin the Festival to preserve their magic, and also to 'purify' the trees so Celeste never becomes strong enough to unleash hell. Sophie-Anne has basically unearthed a vengeful witch that's been trapped in the magical equivalent of The Lifestream for nearly four centuries.
Hayley will become a HybridIt had previously been established that the baby's blood has the potential of creating new Hybrids; which is a pretty major plot development to be just a throwaway device to drive a wedge between Klaus and Elijah. It's also been established that same blood is in Hayley's system as it had helped heal her on at least one occasion. As such, this will all culminate in Hayley dying at some point and accidentally becoming a Hybrid; either before or as a consequence of childbirth. Incidentally, this helps the show as it resolves the need to have Hayley transform into a wolf at various points of the season, raises Hayley up to the same league as the other main characters in the balance of power to allow her to get more actively involved in the various power struggles, as well as (if she's killed before childbirth) resolve the need to get baby actors to play the child.
Mikael is going to be brought back from the deadHe has been name dropped a few times so it's possible that by either the end of the season or somewhere down the road Mikael will make a return.
Elijah will give Celeste her true deathIt was Klaus' lies that got her killed. And Rebekah killed her when she was possessing Genevieve's friend in 1919. Seems to make sense that he kills her for good.