The season premiere took the familiar trappings of Lost and tossed them upside-down and sideways. This is not particularly surprising, but it does leave the true nature of the narrative structure and purpose a bit mysterious. Is the "Loxt X" timeline meant to feed into the "Lost Prime" timeline somewhere down the road, or is "Lost X" just an extended example of how "course correction" works in the "Lost" universe?
The more events in "Lost X" are revealed, the more it seems that all the differences still result in similar interactions. Ethan is still involved in treating Claire and her pregnancy. Claire chooses the name Aaron for her son. Kate befriends Claire, and Kate even seemed to be forming a kind of bond with Aaron. Kate uses the false identity "Joan Hart". These are just some of the obvious connections between "Lost X" and "Lost Prim"; others may be found in repeated viewings and closer inspection. (It should be noted that the ultrasound showed the date 22 Oct 2004, which settles the debate over when the events of "Lost X' take place, even if it is a month later than one would expect.)
The argument against "Lost X" being just a long-term example of "course correction" hinges on the apparent transfer of knowledge of "Lost Prime". Jack seemed to recognize Desmond on the plane in the previous episode, and Claire seems to come up with the name Aaron out of nowhere in this episode. Both could easily be explained within the context of "Lost X' and unrevealed character histories, but such synchronicities are rarely accidental on "Lost".
Of course, the most interesting elements of the episode are covered in the "Lost Prime" universe. Sayid's apparent return from the dead is obviously a major plot point. As predicted in the review for the previous episode, it now seems certain that Sayid is connected in some way to Jacob's rival. This connection is referred to by Dogan and Lennon as an "infection", which harkens back to Danielle's description of what happened to her fellow scientists when they came in contact with the smoke monster.
This could very well resolve one of the loose threads that seemed like it would never be resolved: the "sickness". It seemed like the whole "quarantine" issue with the Swan Station, the vaccines, and Danielle's story would all be dismissed as a matter of mistaken context. Instead, they now all connect to Sayid's circumstance. What happened to Danielle's crewmates seems to be happening with Sayid now.
Dogan's revelation that the same thing happened to Claire fits what little was shown at the end of the fourth season. Claire was "taken" by Christian, who based on his manipulation of Locke at the same time, was clearly a form taken by Jacob's rival. This fits the pattern that Jacob's rival, as the smoke monster, can take on the form of those who are dead. On the island, it appears that the dead themselves can be "inhabited" by Jacob's rival.
A lot is going to have to be clarified in Claire's backstory from the time after the attack on New Otherton to this point. She's slipped into a pseudo-Danielle mode, setting traps and living on the land, and like Sayid, she clearly has a corporeal form. So did Jacob's rival kill Claire and then bring her back to life, as seems to have happened with Danielle's crew? Claire seemed to be alive and well mere hours and days after disappearing in the fourth season, so it's not a long process.
There may be an even more interesting connection. Dogan suggests that Jack and the other survivors of Oceanic 815 were brought to the island for a purpose, which has always been an underlying subtext. For that reason, it always felt like Desmond's role in bringing down Oceanic 815 didn't add up; it couldn't have been a simple coincidence, especially with the plane being so far off course. But what if Kelvin was influenced to distract Desmond at just the right time? Kelvin could have been"infected", especially since Jacob's rival seemed to suggest, in the previous episode, that he was hoping one of the Oceanic survivors would be suited to manipulation. (On the other hand, based on the conversation between Jacob and his rival in "The Incident", it could have been Jacob, and his rival was just taking advantage of the situation.)
Whatever the case, the implication is once again on the table: the crash of Oceanic 815 was no accident. It served a greater design. While previous theories pointed to Widmore, this new spin on the same story doesn't preclude his involvement. After all, the war between Ben and Widmore is looking more and more like a"war by proxy" between Jacob and his rival.
As if Sayid's status wasn't concerning enough, there's the small matter of Claire and her ability to "spread the infection". It seems rather plain that Jin, Sawyer, and Kate could come into contact with Claire, and could very well end up "tainted" by Jacob's rival. With the equal potential for some of the survivors and Others in contact with Sayid becoming "infected", it could be that Danielle's very early prediction that the JackLocke Tribe would eventually turn on one another might come to pass.
But beyond the very welcome return of the gorgeous Emilie de Ravin to the series, the events of "Lost X" are a reminder that there was something important about Aaron. More to the point, things were going to go very, very wrong if Aaron was "raised by another". While this was implied to be a ruse, it certainly doesn't seem to be the case now. In fact, if Claire was "tainted" by Jacob's rival, then Kate's vision of Claire off the island was very likely Jacob's rival himself. Why would he have wanted Aaron to not come back to the island? It's almost certainly connected to the same reason why Claire was warned not to separate from Aaron in the first place.
For that reason, it seems odd that this episode title suggests that this is a Kate-centric tale. While Kate factors into the plot in both timelines, the most important connections appear to be Claire-centric. This wouldn't be the first time that a Kate-centric episode had less to do with her than someone else, and it is a little disappointing to think that the welcome advancements in her character in the fifth season didn't receive a more direct exploration.
Overall, for an episode that didn't seem to have very much action, a great many connections were implied. There's still plenty of room for interpretation, but the big picture is forming, and with quite a few episodes left, there's enough time to deal with the finer details.