Great idea. I don't do large circles, so currently have no need to make one, however, if and when I do, I would consider a minor change. As we all know, FD blades have their sharp teeth on the right, as you face it. (The kerf.) I am currently working on a fret piece with a lot of small INSIDE holes. The blades work much better cutting out an inside circle if you spin the wood counter-clockwise, putting the sharp teeth on the outside of the circle.
Don't know if it matters on circles the size you are making, but if I were to make your jig, I would consider putting the center pivot on the other side.
Just my 1 1/2 cents worth.
jerry