Here is 1979 BMW R100 RT from South Africa. The bike was rebuilt with an option for two seats: the solo one you see in the pictures and the bigger one that can be mounted after bolting back the rear section of the frame. Seems really practical if you don't want to compromise.
The look is complete and clean, no extra wires hanging anywhere, everything is thoroughly organized and hidden if possible. Take a look the exhaust design. It goes well with an old style BMW boxer engine and doesn't overwhelm it with unnecessary details. Curves of the pipes lightly continue those of the frame and naturally fit the overall style. The pipes are routed nicely under the tank.
Here is RT100 from another angle.