Eevee is referred to as the evolution Pokemon. I'm honestly surprised more haven't been discovered. There are plenty of other types that Eevee could be potentially exposed to concentrated essence of. A metal coat helps species like Onix and Scyther evolve into Steel-type forms, for example. Why not Eevee?

Likewise, dragon scales help Seadra evolve into a dragon type. Why not Eevee?