We're told by a couple of people at Canon that the 120mp DSLR concept that was shown this week at Canon EXPO is at least 2 years away. That would put such a camera off until 2017 at the earliest.
I asked if the 120MP DSLR would be in a 1D or 5D body and was told that probably wouldn't be decided for quite some time. Where such a camera would fit into the marketplace will dictate the ergonomic requirements in the end.
A source outside of Canon said to expect new lens development to be accelerated over the next few years in preparation for such a camera as well as “other projects” currently on the go. The same source also said there are a lot of new lens designs in the pipeline and not as many direct replacements as one might think there would be.