You might be able to do something along those lines, but I know of no font / vector 2D renderer that does so. There is a lot of literature[1] on this, so I suspect if doing things similar to subdivision surfaces were viable for font rendering, it would have been explored by now.
I'm a bit confused. Can't you send the shape of O as a low res rough band (a closed wide loop) and enhance it in the mesh shader? This is how previous generation tessellation shaders and sub-division surfaces worked.