This would be my preferred option. ..
This idea is so good, I can't believe Canon are not already working on such a system.
If not canon, then the competition, and then canon... Either way, we win, sooner or later.
My only reluctance is that canon, being mass market driven, finds more profits in selling compromise vs. ultra high end gear. When you figure that for phase one the chip itself is roughly half the price of the camera (it has to be), then unless you have more than $10,000 invested in lens, the offset of saving a few lenses is mute. Is it enough to consider a complete switch and sell off the old system?
In fact, considering the cost of home scanning tabletop solutions and developing negatives in your kitchen sink, would spending an extra $20K make sense for a low volume shooter? Therefore canon obviously sells a compromise, as the prosumer can have a 21MP, right off the shelf at Best Buy.
Truth is, I can't justify a $25K chipset, as the 40d and 1ds cover 90% of my needs. I can easily purchase a film solution from Ebay for less than my current kit for the few images that I need to print at 30", (and continue to enjoy that unpredictable experience).
So I will wait and get my moneys worth from the 40d, and shoot a little film and maybe in a few more product cycles we'll have something worth upgrade to. More pixels is greats. But it's the same quality image, only larger.