Well, (as you may know already) at the moment Inkscape doesn't make circles by making a circle or an arc. Instead it relies on custom attributes to store the properties of a circle.
That's technically correct. A solution would be to finally implement the boolean ops LPE and apply them automagically to the selected path, that way circles could be integrated into the path and being easily manipulated with the circle/arc tool at the same time.
So if you wanted to be able to make a subpath that looks and behaves (UI-wise) as a circle I think it may definitely be non-trivial. (Although it would obviously depend a lot on how much of the UI could be reused.) But I'd love to be proved wrong, I've also long wanted to be able to edit arcs in the node tool for example.
For the time being, maybe it would be enough to add the shapes (spirals, arcs, squares...) to the path even if that means losing some of the control, for instance: turning a circle into a sector would be impossible, but it would avoid a lot of work specially for clipping paths as the poster pointed out.