I guess $70K 2015 Tahoe LTZ's isn't enough....who will be "the market" for VERY high-end 4-door sedans wearing a Bowtie?
Oh yeah...somebody's already doing that!
The others who might play in this arena, including SLP (already mentioned) and Lingenfelter, make no mention of the Chevy SS, but they are doing plenty that is applicable to some degree. I can only think of couple of reasons that make any sense--despite what has already been done by Callaway & Hennessey.
Callaway has typically offered the most refined level of development, though not always fastest or quickest outright, but I think a CSV program would trump that, just by it's ability to get advertising support from within GM, and even if it largely duplicates everything Callaway typically does to their vehicles.
What I'm thinking is that GM has possibly "warned off" any company who had any intentions of doing an SS sedan upgrade package as part of the negotiations with HSV/Walkinshaw, as the SS would be the logical platform to use to introduce the CSV program, with the LSA engine, MRC suspension, and HSV's current line of wheels, trim, etc. Put another way, GM would effectively want to thwart it's competition in the performance upfitting market.
The other scenario is that there is a great deal of focus now on the GenV V8, so Corvette C7 and the newest trucks somewhat overshadow the SS/GenIV, and that's why there's no SLP version of the SS (yet).