You might as well call it anti-surface. This should be a sub-brep type of object that will create openings.
The difference between this object and trims is that it will have exposed control points and you can redefine it programatically or visually.
a brep box made solely by 6 anti-surfaces and combined with a brep box with larger scale and same CoG location would create kind of a Tesseract-ish. Closed box with a hole in the middle That can only be seen when clipped, trimmed, split or in a drawing as hidden lines (make 2d)
This new type will unlock huge amount of parametric workflows.