The Mamiya ZD camera has been on sale in Europe for some time now, and it actually works.
Yes. I tried it, didn't like it and went out and bought the Aptus 75 with all the expense that entails. Actually I tried the ZD the same day as the A75.
As I look back through my image library the one thing I regret is buying the Kodak SLR-C as many of the shots I took with it are unusable. If I had paid the extra for a 1Ds they would have been OK. Buy cheap, buy twice.
In general you are right about prices coming down. But a pixel is not a pixel. Otherwise we'd all be using compact cameras.
The day I can get the quality of a Schneider 35XL digitar on a Canon 1DsIII (with the same degree of movements) will be the day that Leaf et al are truly threatened. Personally I don't think that will ever happen for commercial and technical reasons.
Perhaps MF cameras may need to become more expensive, not less, to handle the increased competition at the 'low' end.
eg: Broncolour flash packs cost $9000 but their business is not threatened by the release of a new hotshoe flash.
This may be a golden age of cheap MF digital equipment!