I have been working with AutoCAD Architecture AEC Spaces for years. They are a polyline’like object with a boundary (which since 2004 could be edited with grips Polylines got in 2011) and hatch fill. Spaces have an Osnap’able centre which is rather useful for placing tags (the default location if you just hit enter when tagging), mirroring or centre aligning content in a space. Even irregular spaces have this “centre” based on their bounding box extents.
Today I was editing a closed Polyline and tried to manipulate it with a centre OSNAP. Of course it doesn’t have one but, given it’s so useful, I wonder why not?