GMPP will supposedly offer a catback exhaust, free-flowing airbox, suspension kit, different wheels, and some other options at launch.
Mallett has an LS2 conversion in the works.
Procharger is apparently working on a kit (though we've only heard that from one source, I think)
There's a company in Utah that should be working on a rear-mounted turbo kit.
These are the quick and dirty answers I can come up with from the top of my head. It looks like aftermarket support will be pretty strong for this car. More info on all of this should be available if you do a search.