As the technology developes the weight of a disc equipped bike will come down more. I don't know what the difference can be now, but disc wheels can use a lighter rim with no brake track. People say the fork needs to be stronger but I don't really know about all that. I do know that the UCI has made an anouncement that discs will be legal in the pro peloton for at least one race, I think next season. This will be interesting.
I think the pro-tour bikes will still easily make minimum weight, even with the discs, which is around 15 pounds.