IIRC the cobras moved the brake disks inboard on the independent rear suspension to reduce unsprung weight further.
I always liked the Dave Cloud dolphin setup. Motor shafts in line with the rear swingarm pivot, one motor on each rear wheel, simple chain and sprocket, minimal unsprung weight and cost and complications. Little jacking but no biggie.
I suppose a combination sprocket/brake disk would be asking for trouble
