Given the nature of some of the major spills I gotta say that the issue of the sharp edge is a valid concern. Of course a rule mandating smooth edge rotors would avoid this.

As you say I seriously doubt that the darn good rim brakes we have are any sort of issue. And frankly I think most folks that are seriously into road bikes prefer the cleaner look of the rim brake style. Not to mention that it would be hard, but not impossible, to bring the weight of the rotor and caliper combo along with the more complex hub down to match the current rim brake setup. The problem is that it would have to be done with rather exotic materials and techniques. And even then I doubt it would be easy.

Frankly from where I sit rim brakes on pukka road bikes are the way to go. I see no significant advantage to switching. Just added cost, complexity and weight.