We’re in la-la land in lost theorizing here.  I think its important to separate two entities: Jacob and Island.  Similar to the hieroglyph when Ben was being judged, there was a figure (Jacob) and the Smoke Monster (Island) always intertwined with each other. 

The Island == Smokey boils down to this, the island can manifest itself as a projection after initial scan by cerebus/smokey.  Locke was scanned, as was Eko and Ben.  Eko’s projection was his brother Yemi, and Ben’s was his daughter Alex.  Locke’s projection has been hidden from the viewers, but could be Christian.  Weak point in this theory is Christian has been projected to other people besides Jack/Locke (also Sun and Frank).  But I think the idea that Cerebus/Smokey is tied to an ancient manifestation of ‘The Island’ holds up through all episodes.

Jacob seems to be separate entity from the Island, and in my mind boils down to three possiblities: Jack, Locke, or no one.

Jacob::Jack – similar names, an interesting destiny if Jack ends up being at the bottom of all the time manipulation.  If Jacob/Island have some mystical ties, then a manifestation of Christian makes a bit of sense, its Jacob using his significant person (i.e. Yemi, Alex) to project to important people to keep them on the past.  Loopy, but not off the map with regards to Lost. At some point we need to be Jack back far enough in time to fill this role. The upcoming incident could toss Jack back far enough in time to be there to influence Richard in 1954.  If the incident happens (and we know something happens pre-1980) tossing someone backwards could be the equal/opposite reaction to get people back in they’re correct time.  Also those around Jacob are also those close to Jack: Christian and Claire.  Could Rose and Bernard also be collected and protected by Jacob?  (okay putting on the breaks here)

Jacob::Locke – The age long mystical connection of Locke with the Island has always been because Locke is Jacob.  The moving of the pieces last episode could end up putting Locke in the same location as Jack’s emergent Hydrogen bomb, and the effects of the Incident could just as well pull Locke back in time distant enough to become Jacob in the past.  This would be so Lostian to have present day Locke confronting himself in this seasons finale, and mirroring the foreshadowing of Locke uncloaking next to the fire.  It’s a cliché  for certain, so it might be one big writer head fake to go down this rabbit hole.

Jacob::No one – This one is emergent in my mind after last night’s episode and the collusion between Richard and Ben.  Remember Richard was Ben’s first connection to the Others/Hostiles. Also Richard played the ‘Jacob’ card with Charles Widmore more than once in the past.  So this requires Richard to be back far enough in time (Black Rock Sailor) to tap into the island’s healing power and survive long enough to always have an influence over various power brokers on the island over time.  Which I could foresee as a couple of Richard-centric episodes that track this manipulation with Ben coming alongside Richard and playing ‘the Man Behind the Curtain’ (an old Ben centric episode that just BEGS to be rewatched now).

I find that its important to match theories against how the writers/producers have told the story up til now, the time-shifting has always been a part of the storytelling, so to have it cease at the end of this season would be uncharacteristic. So I think we’ll get even more intertwined into the time shifting story, and maybe this finale will break off some of the characters that are chaff to the main storyline.  I don’t think the ‘plane landing safely in Los Angeles’ angle is going to play out.