With the series finale, the writers and producers of "Lost" reaffirmed that the focus of the story was the characters' journey; the island and all its oddities were little more than a metaphor, a mirror in which the true selves of the characters were revealed.
It's hard to say just what this epilogue was meant to be, other than a final love letter to the fans. On the one hand, it serves as something of a clever bonus feature regarding certain aspects of the mythology. It's an info-dump, and on many levels, a completely unnecessary one. But by the end, it also reaffirms the fact that "Lost" is about finding one's place in the world and knowing oneself in the process.
The setup is very simple. Ben, as Hurley's "Number Two", is traveling the world, shutting down the remaining Dharma Initiative infrastructure that had been left in place to support the island during Jacob's reign as the Keeper of the Source. After all, the difficulties in finding, reaching, and leaving the island were all the result of Jacob's desire to trap the "smoke monster".
This brings up an interesting point, one raised long before the true nature of Jacob and the Source was revealed. How does an island move and still follow the laws of physics? How can Jacob, as the Keeper, set the kind of rules that applied over the entire course of the story, yet be consistent enough for Daniel Faraday to apply his revolutionary theories from the fringe of quantum physics?
One might argue that the entire fifth season was a long and complicated lesson in Daniel's fallibility; Daniel made the assumption that the island's properties were based in some objective set of physical rules, but that wasn't the case. He recognized the role of the variable, but didn't realize that the only variable in the equation was Jacob. His data was incomplete.
At the same time, this may have been the case because on some fundamental level, Jacob's rules had to be expressed in some quasi-consistent set of physical laws. So while it was an expression of his free will (and therefore variable as a result), the manifestation of that will ultimately follows the laws of physics as much as possible. Call it the path of least resistance, after a fashion; the unnatural largely achieved through the natural.
This wasn't at all mentioned in "New Man in Charge"; it was just something that was brought to mind by the reminder that the island moved, and thus there had to be a means by which the Dharma supply chain managed to account for that. This is spelled out in this epilogue, but one has to wonder if it was really all that necessary to do so. It was clear that the island was tracked by the Lamppost, that computers were involved, and that there was still a Dharma infrastructure of some kind in place. Did the source of the supply drops really need to be further explained?
Perhaps it did; certainly they felt the need to spell out the answer to the polar bear question, despite the fact that all that information was already evident by the start of the third season. The Hydra orientation video was a clever way to frame the exposition, but again, it basically made it feel like a clever concept for a bonus feature devoted to spelling out what most viewers should have been able to figure out from context.
(As an aside, this is an example of the producers giving the audience exactly what they wanted, and making a pretty good case for why this wouldn't have worked in an actual episode. As a gift to the fans as a DVD extra, this kind of heavy-handed exposition is fine. But it would have been hard to pull off in a regular episode, where the focus was on discrete, episodic character exploration as well. There's a reason the orientation films were usually cut down to the bare minimum!)
The Hydra orientation film was chock full of little connections to help the more mythology-oriented fans find some closure. Again, this applies only to the ones that couldn't reconcile putting the puzzle pieces together on their own. All this information was either directly or indirectly revealed over the course of the series. In some cases, it takes something that was contextually evident and states it bluntly. Very bluntly.
While I am being a bit critical and skeptical of the need for such a direct set of explanations, as a fan of the Dharma mythology, this was a nice look into that aspect of the "Lost" universe. A lot was covered, but if there was one element that was most appreciated, it was the confirmation that the energies of the Source were related to the gestational problems that plagued the Others after the Incident.
Of course, the exact explanation is, itself, something of an implication. Dr. Chang says, point blank, that the experiments with polar bears at the Orchid involved the unusual electromagnetic properties of the energy there (tied during the series to the Source, of course). He then warns that pregnant polar bears shouldn't be exposed to the Orchid, because this can cause the infamous gestational problems.
Unfortunately, that doesn't track with the problem encountered by the Others. If a woman was already pregnant before coming to the island, they were fine. The problem was associated with both conception and gestation on the island. The bizarre time-altering nature of the Source, tapped within the Orchid, certainly factors into that, now that it is absolutely clear that the Incident did take place. The old theory still holds. It's the quick explanation that doesn't quite add up.
It's similar to the problem with the "whispers" explanation given in "Everybody Loves Hugo". It sounds good at first, but it doesn't match what was shown and said previously. It's the kind of retcon that really isn't necessary. But if this epilogue does serve one purpose, much closer to the theme of the series as a whole, it is how they address Walt.
In the review for "Across the Sea", I noted that the offhand comments about Jacob's brother being "special" effectively resolved the entire question of Walt's purpose on the show. The Keepers of the Source seek out those with unusual abilities that can serve as their replacements. Walt was definitely among the Candidates at the beginning of the series.
Being "special" often had a very specific meaning on "Lost", though it manifested in several other ways, depending on the individual. In essence, the specific sign was the ability to see and communicate with the spirits on the island. That quality provides the basis for the resolution to Walt's character arc. Instead of being lost and purposeless, Hurley and Ben offer him the chance to use his gifts to help those trapped on the island.
It's a nice way to address the fact that they couldn't get Michael and Walt into the finale, while also adhering to the spirit of the series as a whole. It takes what was mostly an info dump and returns it to the character-based premise of finding oneself. And it also gives the fans a glimpse into the Hurley/Ben era, and how Hurley is slowly but surely changing the rules that Jacob set.
The Dharma infrastructure is no longer needed because Hurley has made it possible to come and go from the island without apparent restriction, as hinted in "The End". And now he intends to give Walt a purpose by finding a way to release those trapped on the island. There's still the hint of manipulation on the part of the island's protectors, but it seems a lot more benevolent than Jacob's machinations turned out to be.
In the end, does the epilogue serve its purpose? That depends on what one imagines that purpose to have been. If one is looking for the answers to every lingering question pertaining to the mythology, then nothing less than a 10-hour point-for-point Q&A with Damon and Carlton is likely to satisfy. If one is looking for one last pleasant slice of new "Lost" content, as a final farewell to the dedicated, then this does the trick.