Disc brakes on road bikes are going to cause some compromises. The compromise that worries me the most is fork stiffness. If a disc brake was mounted to a standard road racing bike, the fork would twist during braking -- that's a lot worse than the squeal of poorly adjusted cantilever brakes. For a road bike to have the smooth, buttery feel that people seek in road bikes, the fork has to be pretty flexible. Making the fork stiff enough for a disc brake kills its ability to absorb small bumps in the road. Many touring and cyclocross bikes have already given up on that bit of suspension, opting for stiff forks and wide tires. MTB suspension forks are extremely stiff in torsion, so adding disc brakes doesn't make a difference for them.

How about replaceable braking surfaces on road rims? Can we have those instead of disc brakes?