So I have a theory about Walt. The way I understood his power was that he had some sort of preconscious ability to will things into existence.
So when Ben and Hurley show up and tempt him with the possibility of redeeming Michael, who Hurley knows is stuck as a voice on the island, Walt obviously agrees. The question remains though how else could Walt save his father, other than to help the new owners of the island create their post-life waiting world. Put walt near the source and have him wish extra hard. Bam, FSW.
Personally I like this, because now if you're trying to discern the means by which Hurley and Ben somehow create the FSW, you don't need to somehow weave jughead's explosion into the equation, as thats a huge stretch. This way, its through Walts power. and this was his fate ALL ALONG. SO all in all, this epilogue, at least the part that wasn't taunting fans in the smuggest possible way, has bridged the gap between post island doings, and the FSW, albeit vaguely. ALl the while tying up Walt, who so many fans were disappointed had to be effectively written out.