it will be interesting what upgrade-options Leica will offer to existing customers, Hasselblad is very active in this regard.
Personally, I won’t invest in a S3 anyway, not only because the price is somewhat to high to justify it, but also because I’m more than happy with the S2 (also compared to the newer Nikons).
What I could imagine, is maybe a kind of S-monochrom. This will need almost no investment from Leica, using the same sensor as for the S2, giving all the benefits of pure B&W.
And there are probably some serious B&W-photographers who will apreciate this variant. I certainly would, but I’m not sure if I can handle a second body (financially). But what a great picture this can be then!