In some ways it could be argued that it's a possibility. Changes in climate don't really account for all the major differences though. For one thing if Etherealists were just Fury Crafters, than everyone would be a Fury Crafter. All humans had access to Fury Crafting, Etherrealists are unique among other humans. Plus it doesn't even seem to work the same way as Fury Crafting did, on top of that the insanity that comes with being an Etherrealist is of course not shared by Fury Crafters.