And what if the programmer is already using the stencil buffer for something else? Besides which, do you even know where stencil test runs in the pipeline relative to clipping and polygon division? Or that stencil test is dependent on clipping and polygon division? You really haven't thought this through at all, have you?Therefore the stencil-buffer is existing
You're now moving well away from "direct support" and towards "crutched up by a load of fragile hacks that are going to break if you even look funny at them".