That'd be incredibly complicated...an entirely different (and like twice as big) set of rules that we have to keep in mind...
I don't think they would do that because it would be too complicated for the kids to understand (I didn't know all of the type effectivenesses until I joined smogon xD)
This is true.
GF creates game mechanics that would be easy for a 10 year old to understand, but enjoyable and complex enough for a late teen to be able to play also