To be clear
Teemo is a prototypical male Yordle, Tristana is a prototypical female.
Yordles do have a lot of variety but we will probably not release another heimer or corki. Ziggs is a good example of a unique looking Yordle who still looks like a Yordle. We prefer this approach.
This is intention but you never know if someone comes up with an awesome new Yordle variation we would do it,.