When Jacob describes the island and its purpose to Richard, he describes it as the focal point that keeps all evil from totally overwhelming the world.
Is the island located in another dimension that is only accessible from a certain point in the Earth's physical ocean; hence the pendulum at the Lamp Post station and needing to follow a specific heading on the ocean to reach it?
Or is it a physical island on Earth that moves simply due to the kind of place it is?
My interpratation to LOST is that the Island is a time machine that housed life extension in every concievable way -- and it's purpose was spiritual in that it 'properly motivated' variable sets (groups of people) to save the Island through interactions with smoke monster astral projecting "black hats" aka antagonistic roles, (including MIB to motivate Jacob), which in turn perserved an astral plane (the flash sideways), which is the process for reincarnation and multiple iterations of any given timeline.
In other words viewers witnessed one iteration/go around of the timeline, but with hints of previous iterations as the Island has to network the timelines to keep the fabric of the universe from breaking down, although we saw the beginnings of new one they made when they time travled back to the 1970's, creating a branch off, which was reflected in the flash sideways, providing a glimpse of the upcomming 2004. It operated with Alice in Wonderland like dream logic, where the characters had to see the conections to it by remembering the past, before moving on. Others will still have to deal with the Island in the next go around, as this was the point of Ben not doing so--he believed he didn't deserve that life yet.
So although I do think it may have moved between real places interdimensionally, it always was on Earth IMO, otherwise Charles Widmore could never have found it. It's just that the Island can switch locations and does physically move and the Lamp Post Station has the means to track it. I'm not saying that it couldn't of, just that there is not a lot of evidence to support it.
However, I'm inclinded to rethink it. A lot of Bad Robot works tend to reference eachother and touch on the same subject matter. So your Q made me think of pocket universes and that made me think of one particular episode of Fringe that also shares LOST's Alice in Wonderland references.
In the season 5 episode, Through the Looking Glass and What Walter Found There, there is a hidden pocket universe that Walter is trying to remember how to get to, because he believes that might be where Micheal is hidden.
But the way to get there is inside this rundown old apratment building, but he has to do a series of "steps" and turns in order to get inside the pocket universe, which in turn is a mirrored apartment building.
Meanwhile, Walter (John Noble) continues to work at extracting video tapes from the ambered part of the lab. One tape directs him to an apartment building in Worcester, with one specific apartment being an entrance to a pocket universe he has created to hide this element of the plan to defeat the Observers. He decides to travel there alone, finding that the building and much of the surrounding area has been shelled by an Observer attack in the past. In the appropriate apartment, Walter follows instructions on the tape that let him enter the pocket universe where the normal rules of physics do not apply, with hallways running upside down or in vertical directions, as in a work of M.C. Escher. Walter tries to remember where to look, but while trying to come up with this, he encounters a man named Cecil (Zak Santiago) who happened into the pocket universe while taking shelter from the Observer bombing. Walter realizes that, to Cecil, only about 5 days have passed, but in reality he has been in the pocket universe for more than 20 years. https://en.wikipedia.org/wiki/Through_the_Looking_Glass_and_What_Walter_Found_There
So there is some commonality there, but LOST's physics I think were more about keeping the fabric from breaking down (ie: not letting guns fire, people surviving 8 story falls, ect) since time travel factors into the mechanics, as opposed to seeing something more fantasitcally defying.
