Concerning the X & Y pieces. Yes, it's simply a different jet size. But.....the majority of people (myself included) would rather just change the whole piece rather than mess around pulling old jets out and pressing new jets in, only to then break the piece and be worse off then when they started.

Jets would be removable so that people like Stephen can play with them.

Mold is designed, just gotta make it and cast the parts up.