There are few unnecessary lines and creases to create a clean, taut shape. It does look a bit less athletic due to the notchback look that comes with the soft top. It causes the tail to look much larger and heavier than on the coupe, and it reduces the amount of glass area even further.
We suspect this is an M variant due to the quad exhaust tips and large brakes with blue calipers. The wheels are different from any other prototype we've seen, though. Since this is likely an M car, it should have a very powerful engine under the hood. But as we've learned, the 8 Series will not feature a V12. This means it will probably have a twin-turbo V8, and the logical choice would be the 4.4-liter version launched in the new M5. That would mean at least 600 horsepower and 553 pound-feet of torque. Our spy photographer predicts power could reach 650 horsepower, in part to differentiate it from the lower-end M5. It would also allow some breathing room for future M6 vehicles. On the other hand, BMW said fairly explicitly that its M cars would be capped at 600 horsepower. We'll see whether the cap or model differentiation wins out.