This is a good initiative by AMD, though the multicore chips have been here for some time it's been hampered by the different software paradigms fighting for the programming model. Some standardisation with tools support will give it the much needed push and breakthrough.
Samsung has also reportedly joined.
This is the kind of really big fish they need.
As I understand it HSA will basically write an API that software developers COULD use in multicore AMD or ARM SoCs if it is supported. So they really need to get some big SoC and systems designers like Samsung into the club if it will have any cred.