I made a video log if anyone is interested about how they ended the show and what I would have liked in season 6, given how they wanted to end it.
summary: they opted to leave mysteries mysteries, and that's fine. So many elements are grabbed from forteana anyway, and are unanswerable, this is simply their take on that issue.
Nevertheless, I got the impression from the first three seasons they'd be tying these enigmas into a narrative whole... and though they didn't, it's still quite possible to do so, and speculate how it might have been done. I would have liked season 6, if this was to be about moving on, to be about the Whisperers. Instead of the dead showing up in LAX/FST, they'd have showed up as whisperers on the island, initially thinking they were living, but eventually figuring out they were not, helping the living (as we've seen) and trying to get to the light.
There is the link above, or if it embedss.