A duplex 5-20R would be easy to split into 2 separate circuits. A 2-pole breaker would easily do the job with 3-wire cable for shared neutral, or 4-wire cable for split neutral. For the latter, you'll need to find dual circuit cable since you can't remark the blue wire of three phase cable as an extra neutral per 200.6(A). I suppose you could also do it with one of those duplex breakers (no shared neutral, must be split neutral only) if the panel accepts them and you can find a way to tie the handles together (I haven't seen that).
A duplex 6-20R would be a lot harder to split into 2 separate circuits, since you'll need to find a 4-pole breaker. Maybe one of those 2-pole duplex breakers (Cutler-Hammer has them in the BR series) with some kind of handle tie over all 4 handles (I haven't seen that).
What does "at the point where the branch circuits originate" in 210.7(B)? There is similar wording in 210.4(B). Does that mean the actual breakers in the panel? What if I put a 40A 2-pole breaker in the panel and feed that to a small subpanel immediately adjacent to the main panel with a pair of 20A 2-pole breakers. Would the one 40A 2-pole breaker meet the requirement of 210.7(B), or does it have to be the last point where circuits branch out at breakers?
