HKS is not sitting on their butts. I have the HKS ES Premium on my car. The question is will you pay north of $1500 for the system. If you want the system, go to your authorized HKS dealer and have them contact HKS USA to order. It should be available in the US shortly.
Greddy is busy with development, but they are also planning to make an exhaust system for the STI as well. The Greddy system is also likely to be north of $1k.