OK so I posted this as a sorta "quasi-theory" in another comments section, to answer someone's rather snide questioning of how could it possibly be another version of "real Locke" in the finale, and that we just are led to believe it is "Fake"Locke.
First a couple of things to set this up:
1 In the past we were led to believe that Jacob resides in the Cabin, but now after the revelation in The Incident we now know that "Someone else has been using it" and that "He hasn't been here for a while" So with that we can all agree that MIB is and has been using the cabin, and or was trapped in there.
That leads me to another point:
2 In The Man Behind the Curtain We see John Locke interact with someone that Ben clearly cannot see or hear, I believe that man in the rocking chair was the MIB, He is somehow only visible to John. (Keep this in mind)
3 How would we likely see two of something or someone on the Island at the same time? Well one way is time-travel, as another Theorist put it we did see Sawyer watching Kate and Claire "Birthin' the Baby" while time jumping, and we know from the actual episode that Sawyer was on the beach when Aaron was born, and while Boone was dying, So theoretically there must have been two Sawyers on the island at that particular time. Same goes for John Locke, when he sees the Hatch light go up in the sky, he knows that he in a past form is over there cryin' his eyes out and having a pity party, so there again are two Lockes on the island at the same time.
Another way would be if the FDW was to time-clone the person turning it, (this of course is only a question due to the deleted scenes in season four's DVD the scene in question is called The Stash) But I won't get to deep in this, the gist is (this is both scenes put together the actual and the deleted) that Ben turned the wheel and woke up in Tunisia, beat the crap out of the Bedouins and then stole the horse only, to ride a mile or so away to another site were there is a well, to get his Stash (Passports and money)out of the stones of the well, now for some unknown reason the camera pans to a wide shot to reveal what can only be described as another version of Ben, Still in his "Haliwax" jacket complete with furry hood, and still wearing the same dungarees that he currently has on as he observes himself, lying on the ground pre-waking-up! So if that scene does mean anything then it would be possible that the same thing happened to Locke
The other way to Get another version of yourself to the island without using time travel or Donkey wheels, would be; Alt Realities. If there are two Lockes on the Island then it theoretically could be that also.
But anyway, this theory isn't so much about the how are there two Lockes, as it is about the why does it seem that Locke (or his body, or a copy of his body that is), is being possessed or indwelt by the MIB, and this also is in my opinion the only way to explain the mystery of "Is Smokey and the MIB the same guy?"
otherwise the two are mutually exclusive, that or Smokey is omni-present/ubiquitous.
So here we go now for the good stuff!
Taking into account the fact that Locke was the only guy who could see MIB in the cabin, and that Ben couldn't see or hear him, then might it be possible that nobody else can see or hear MIB except who he wants to see or hear him? If this be true, then might it also be possible that MIB is not living in the dead body of, or even copying the dead body of, John Locke, but is merely guiding him and informing him invisibly and only John can see him? So it seems to everyone and us that John just knows things when really he, as he told Sun, is the "Same man he's always been".
Ahh!!... Didn't think about that one did ya?
Ok so just for arguments sake lets say this is true, now if it is, then there would be no reason why MIB cannot also be Smokey, or MIB also be Christian, (I know I know, I'm like the biggest opponent to this idea, but that was before I thought of this, and keep in mind this is really the only way[unless someone can come up with something better] it could possibly be to have MIB also be Smokey), you see, if he is only secretly guiding "John version 2.0" invisibly, then he can most certainly tell John he has something else to do, and to just sit here and wait for Ben to wake up, (Dead is Dead) so he (MIB/Smokey) can then leave John to watch over Ben, while he cuts Sun and Frank off at the pass,(Namaste). When Sun and Frank arrive at the dock of the Main Island, in this episode, they hear the noises of Smokey and see the trees moving, Frank makes some sorta remark about wild animals or something, but Sun looks like she knows whats up, any way soon afte! r we get to see Sun and Frank meet Christian,(Who is definitely Smokey this whole time), But this is where we as the audience get confused in hindsight, because since The Incident we have thought that Locke was MIB and before that we thought he was Smokey, so that led a lot of people to believe that MIB and Smokey were one and the same, then the conflicting evidence of; if Flocke/MIB is on hydra island at the same time as Christian/Smokey is on the Main Island, the how can they be the same guy? So that is the answer to that question, if the guy that is invisibly guiding Locke is also Smokey/Christian, then it is possible that he leaves Locke alone for a little while to take care of some other business, then meets back up with Locke soon after or while Ben is "Summoning Smokey", remember Sun said that John went into the Jungle and then Ben told her that he had no control of what walks out of that Jungle, then John comes be-bopping out like he just finished havin! g a nice potty break, well I now think that Smokey/MIB was giv! ing John the "plan" and telling him how to get to the Temple, so that He could set Ben up for the fall.
Now for the big finish:
If all this is theoretically possible, then might it also be possible that after Richard slides the rock out of the way and (F)Locke and Ben enter the statue that Jacob actually recognizes MIB (as he can see him too) and that he is actually "Speaking" to the invisible MIB, and not Locke as it seems to us and Ben? And if this is possible then there may be a clue to this in what John replies when Ben remarks, "I take you two have met?" (He like us is assuming that Jacob was "Speaking" to John when really he is "Speaking" to MIB) John replies "In a manner of 'Speaking'" (as in he is speaking for the MIB now, so yes they [MIB and Jacob] have met) but John is just the mouthpiece for MIB.
So let me know what you think, I'm not 100% sold on this idea myself it's just something that popped into my head yesterday and I thought it would make a good theory of how, if at all, Locke is really Locke, and MIB is also Christian/Smokey.
Thanks, Your fellow "Lost nerd"
Rick