The important guys all have the special numbers, which add up to 108. That would imply that whoever is at 108 might be the most important one of all, as seemed to be suggested about Walt in the beginning of the show, and plainly "108" was who Jacob needs to come to the island and will have to find another way. Interestingly, Wallace is also a first name, for which Wally is a nickname. Wally is also a nickname for Walter. Thin threat I know, but...

And it could still be him, after all. He IS living with his grandmother for the last three years, maybe he's using her maiden name, with both his parents no longer in his life? Or his near-step-fathers name? You would think that he would have attracted some attention if he was known to have been one of the passengers of 815 back when the Oceanic 6 all came home, or when the plane was reported found in the ocean, and while Michael Dawson and Walt Dawson or Walt Lloyd are not exactly uncommon names, you would think someone would have taken note. Also, none of the Six seem to have tracked him down. The only contact I recall being mentioned was his visit to Hurley in the nut hatch, and with "Bentham." Walt being adopted and/or changing his name would make a lot more sense in that context.

Eh, or maybe it's someone new. Thppt. Half a dozen episodes are not going to be enough to wrap up surviving storylines, let alone deal with an entirely new and important character.