I have a feeling it will be of the lightning element. A lot of animes and games made in Japan use the set of fire, water/ice, wind, and lightning, which correspond with the five elements of Chinese tradition (lightning being metal, and wind for wood). Earth usually isn't added.
I suppose it depends on whether W is doing Western or Chinese elements, then. It's quite true that based on the Phillip Memories we've seen so far, it could be either.
(Though if he got one for Lighting/Metal, then it would stand to reason he would eventually get something for Wood to complete the cycle... which is hard to imagine, but could be interesting.)
In Bagua, the wind trigram is associated with the wood element.
For a specific toku example, there is Rainbowman. From Japan Hero:
“Kusaki No Keshin” (Plant Incarnation – Sometimes also identified as a Tree Incarnation) – He is able to strike down opponents using sound-waves generated by his “Tsumuji Kaze No Jitsu” (Gushing Winds Skill). Can also refine these same sound-wave echoes into a mind-piercing screech that can drive his opponents mad with pain (“Kodama Tataki No Jitsu” - Tree Screeching Skill). He is also able to shoot out pine tree leaf-like ‘darts’ at his opponents using his “Matsuba Shuriken” (Pine Tree Shuriken). Using his “Ko No Ha Rai No Jitsu” (Tree Leaf Storm Skill) he is able to create small windstorms of leaves and debris that can blind his opponents.
I think I'm still going with the earth element with fang, since its a dinosaur fossil thing. I also remember lightning being only a subclass of fire in most cultures/religion like Agni, Wicca, etc. Avatar: The Last Airbender even utilizes the lightning as a stronger attack by Azula of the Fire Nation.