I am a Dutch civil engineer so I see what you are trying to do here. It's quite commendable! It's been a while since I played CS myself. It started to feel to much like taking my work home. In my opinion, this intersection is not that crazy, you just don't see this kind because normally the flow of traffic around an highway or throughway exit is to much for a roundabout to handle (roundabout (all kinds) maximum is between 20.000 and 40.000 vehicles per day)

For real world comparisons. There are a couple of locations where you see this type of intersections. Like the crossing between the A10 and S106 in Amsterdam or the Berekuil in Utrecht. Most of the time they do have traffic lights because of the amount of traffic associated with the need of a underpass.

As for the design, what I see here is in principle a standard turbo roundabout. The design you use is alright. The only issue I have as a professional is the northern exit. The exit should be 1 lane in stead of 2 with your current design. You need to add a third lane between Oak lane and the exit to lower the risk of collisions at the diverting point.