What are the methods to auto eject parts (into a collection area/box/basket) in order for the 3D printer to continue printing?

For some reason this feature isn't common (yet?). Is there a hidden reason why?

Will using the print head to ram the part off the build plate into a basket nearby cause the print head to misalign (if using belts).

I am planning to use a Cartesian XY-Head type (like CoreXY) printer, where the build plate moves along the Z axis and XY axes are on the ceiling of the printer using belts to move the print head.