Colnago's wheel spec is 24 spokes f&r. Given the large contribution spokes make to aerodynamic drag, and the fact that road wheels with rim brakes work just fine with 16f/20r, the increased spoke count needed to deal with brake torque might well be the deal breaker for road racing.
Or more simply - a solution looking for a problem
The only advantage that could potentially exist is in the wet where discs will work more effectively than rim brakes but even in wet conditions rim brakes are fine. Off road is different and there are a few problems that they resolve.
Or more simply - a solution looking for a problem
The only advantage that could potentially exist is in the wet where discs will work more effectively than rim brakes but even in wet conditions rim brakes are fine. Off road is different and there are a few problems that they resolve.