I was wondering when these would come out, since it showed up at the Geneva Motor Show.
Considering how good the regular PS4 is(i believe you don't get them in the states?), the PSS needed a replacement. PS4 is remarkably close to PSS on dry conditions, but on the wet it's miles ahead.
From what i've seen the pattern is almost identical to the PS4 so i'd expect the "S" to step up on the dry, maybe losing some wet handling points compared to the standard PS4 and still being an improvement over Super Sport's in everything.
However we have to wait and see if PS4S will be available in smaller sizes, i am not sure the market has enough room for 3 sport/high performance tires (PS4, PS4S and PSC2)... It makes little sense to have something between PS4 and PSC2 right now, so this may lead to the PS4S being just a replacement for the PSS in "supercar" sizes.
It's already on the french site:
http://www.michelin.fr/pneus/michelin-pilot-sport-4-s