Anyone wanting to use this beast off a tripod or without flash is crazy.
I have a P45+ Mamiya combo; it is basically unusable even for outdoor portraits in the Paris winter light. Lack of depth of field and camera shake kill you, off a tripod. The D3x set at 1600 with a fast prime is usable and sharp anywhere. If you can set up a tripod, the P45+ cannot be beat, even a 10MP crop can be enlarged to 44".
The S2's form factor is nice. The camera design is nice. But the slow sensor is obsolete. Leica need to find themselves a better sensor, or that thing will stay on the shelf however good the lenses, which are supposed to be superb.
And, for the record, I have the same issues with my M8, it simply runs out of light all too frequently; camera shake is its worse enemy and if you don't care about shake then you aren't printing big or cropping, and then you don't need those sharp lenses. The M8's sweet spot is 13x18".