Personally I think there's a likely connection between elementals, sprites and the anima we create as part of the anima weapon quest series. It seems it is possible for highly concentrated aether to develop sentience so I wonder if the elementals underwent a similar process, albeit a more natural one. Where our anima was formed by concentrating aether in a weapon I wouldn't be surprised if the elementals were born from a concentration of aether in the trees of the Shroud. Sprites may simply be a non-sentient progenitor form.