The HSA play seeks to increase the number of things that fall into category 3 but it has so far produced very few results.
I think that we have seen the results and know what to expect in most areas, I haven't seen many examples tho, but, I am not looking for them and that could explain part of it.
Spending generations getting APUs to where they provide tangible benefits to a tangible portion of the market is R&D budget, software budget, development time and actual silicon chip transistor budget that could have been spent on other goals (like entering the Phi/CUDA space more aggressively, or lower power CPUs, or more aggressive ARM adoption, or any other number of things).
AMD has been doing that, better OpenCL support, unmatched dGPU compute performance, the "first" ARM 64 bit server, HSA development and more, with less.
Come Skylake low end 720p gameplay with some settings turned up shouldn't be a problem.
720p...? Trinity could do that. Haswell can do that. Aim higher! Hopefully 1080p gaming with some High settings will finally be possible by then?
Those who are already programming for GPU aren't using JAVA and those who don't will struggle to either find a good use case or come up against a high learning curve. Not to mention lack of availability for consumer and enterprise chips. Developing for HSA will take many years to mature and even longer for widespread JRE version adoption.
You don't target "those who are already programming for the GPU", you target people interested in doing so, without having them to learn new things, some who did so natively might convert to higher level code development because it would be faster to develop a product, a service, a system, a prototype. This is the Intel mindset of Phi, but even higher level, and for the same reasons that Phi gets support, this will get support.
HSA hardware support, like everything else, it takes time, if AMD decides to kill the cat cores and only sell Carrizo this year, with its full HSA 1.0 support, its a start for full AMD support in the next 3-5 years, which I think they should do. (Along with Mantle and TrueAudio.)
JRE support, if you need it, you will get it, if they decide to auto update it even sooner, better. Not much different than any other software.