Normally vendors prepare the documentation and SW support tools first, and only after release the HW product on the market. And it is logically based: customers can be prepared to new product, adapt their algorithms and programs to be ready to use benefits of new HW.
Seems GPU producers (and AMD as well) are vendors of another type. I am sure AMD has to have documentation for ISA of SI devices (HD7xxx). Only God knows why they do not give access to this docs for all.
But we have quite good disassemling tools to try document instructions for SI ourselves.
I call all people who need this info to help each other and post here the discovered info about SI ISA.
Maybe this will push AMD to publish this info in more close time.