Interesting post. I think flaperons are not really suited to slow an airplane for landing. If you look at a cross section of a wing and draw a line from the leading edge to the trailing edge you will get an angle of attack (AOA) as compared to the relative wind. When you employ flaperons (both ailerons down) you are increasing the AOA across the whole wing. If there is no wing washout (where the wingtips are twisted to lower the AOA) you can stall the whole wing or tip stall even though the airplane appears straight and level. Flaps are designed to slow an airplane for landing. They increase the AOA only on the inboard section of the wing while the outboard sections (where the ailerons are) have a lower AOA and therefore remain in control.

Spoilerons might be a better way to slow for a landing because by bringing both ailerons up you are lowering the AOA on the whole wing. This would allow you to fly nose high and thereby increasing your induced drag. A harrier approach if you will.