I am a bit sceptical myself, to be honest. I think that the basic idea is good, but execution will determine the success.
I'm afraid that even good execution will leave the camera facing the question, "Why should I buy an unestablished camera for a very large amount of money, when I could buy an industry standard like Hasselblad?" There are a few possible answers -- handiness, perhaps, an extra stop, maybe, but are those answers compelling for the *mass* of MF shooters? I think the real story in MF digital is that the market is small enough, and the money large enough, that eventually one or two companies will survive, and the others will go away. Leica is starting far enough back that it is severely handicapped.
The other advantage to the Hassy-style removable back system is that there are always beginners looking for used equipment, while the pros want to move up to the latest stuff -- so, you sell the old back and buy a new one. With Leica, you sell the whole camera just to get the new sensor. Believe it or not, the box costs something.
Also, to tell the truth, Leica has not been good at cutting-edge tech since the M3; they've simply lost the culture, I'm afraid. They are also behind the curve on software. The M8 (one of which I own) is capable of excellent images, but in many ways, was a kludge. Now it is pretty much obsolete. The Leica forum has a series of comparisons between the Panasonic Micro 4/3 G1 and the Leica M8, which the Leica wins in terms of sharpness using native lenses for both systems, but it doesn't win by much - and the G1 can handle M glass with an adapter, has focus-confirm which eliminates the M's ystem-wide problems with front-and-back focus, and it costs *$600.* That's *one-tenth* the cost of a new M8.2.
I think the S2 may turn out to be Leica's fatal mistake (but, I could be wrong -- maybe the camera will be so good that MF users will be throwing their Hassys into the nearest ditch.) Still, I wish they'd put the money into a EVF/live view/focus-confirming/FF/cutting edge sensor/ rangefinder-styled camera...
Leica reminds me a bit of IBM when the first desktop computers came out -- from a position of dominance in PC production, IBM was always too conservative and expensive, always predicting that X amount of memory was more than anyone could reasonably use, "why would anybody want more than 64K?" and wound up losing their asses to the likes of Dell. Like IBM in the 80's, Leica seems to me to have a culture that simply doesn't understand the new thing.