most deaf people don't see being deaf as a disadvantage, and will get really miffed if you tell them it is. odd but true.
saying, "sorry you can't hear, wouldn't it be great if you could" wouldn't be the right approach, maybe, "wouldn't it be great if we could all communicate with each other... people are divided for so many different reasons, one day we'll all be united, etc." well thats what I'd try to get across if I ever met a person who was deaf and could read lips really good.
Yeah it's a very taboo subject with the deaf, one best left for later. One of the main reasons is because the implants that they have now don't always work and when they do they don't always work correctly, plus they have to pretty much relearn how to communicate. It's totally not a subject you would bring up with the deaf to get them interested. The deaf don't view it as a disability since they have reached the point where they can function just about as well as anyone else.
Right- some deaf people have disowned family members for getting the implants. It's very controversial.