Huh? That's only feasible for intersections of large roads, but American four-way stops are usually on small(ish) residential roads, where single-lane roundabouts work just fine.
No one is saying that roundabouts should replace ALL intersections, and the few they have in small residential places operate just fine with a single lane, but I'm skeptical of their value over a proper 4 way stop or a 4 way protect turn light.