"Canon, Nikon, et al measure their sales volume in the 10,000's and 100,000's." the Canon/Nikon may be an average $2k and MF $15 to $20k?
The consumer market is getting flooded with 6 to 10 megapixel cameras. Is that going to affect the Canon Nikon market? no because 6 mp in a Coolpix is not the same as 6 mp in my S2. Same thing with the 22 MP of the Mk3. This are pixels produced by sensels half the size of my P 25, it would be like a car with half the displacement using an enormous turbo charger to catch up with the cars in the next formula, if the two have same performance then we are in the metaphysical world.
Medium format has, in practical terms, merged with Large Format. I don't see how this new "larger format" would disappear because of the Mk3. Also you cannot mount a Mk3 on a view camera (I mean, not mount it in a satisfying way, the mirror gets in the way of wide angular lenses etc).
Mamiya used to have an entire line of MF systems: The RB, RZ, the 7, the 6 a single lens reflex with interchangeable optics, the 645 PRO and the 645 AF. They will probably not go away just because of Hasselblad. Now they have a solid working relation with a major back company, (Mamiya was acquired by a company that some describe as "the Google of Japan" that can provide the most needed software help --but with Phase I don't see much more need-)
To say that, in the past year, Mamiya was distracted is probably an understatement, the ZD camera/back experiment almost killed them. I don't know what happened to Phase, but Hasselblad has a very aggressive marketing operation going on, so that probably counts too.
Things will definitively get interesting in Q1-08. Major clash of H6y, H3 and the new camera -- I suggest for a nickname PHASE 2 System, or P2 -- so, we can only sit and wait ...