I think I get what AMD is trying to do with HSA. When you think about it, although it is still on the same dye, there are still only four compute cores and 8 graphics cores. What if it weren't so in future generations? What if all 12 cores were simply so heterogeneous that they could swap back and forth between the two? Here me out.
So, let's say you're rendering your video on a (theoretical) future APU and you want openCL acceleration? Well, you toss it onto the APU in openCL mode and now you have 12 cores working to render the video instead of just the 8 that were there previously. Now, obviously now 100% of the performance could be tossed on to that. The APU would have to save some compute power for still managing the system, but what if that is what AMD is going for?
Trying to play CoD ghosts? That game is somewhat cpu intensive. Same as BF4. Well, if you have a dedicated gpu (like say an r9 280x) you use that primarily for cooking up killer graphics and your cpu goes from just the four cores from an a10 7850k to an 8 core or ten core beast and uses the remaining 2 to help boost graphics.
Wanna play MW2 from back in the day? That game does (almost) nothing on the cpu. The computer uses 4 cores on the game and 8 on graphics. It would auto balance it all.
Wanna stream youtube videos or netflix shows in native 4k? Two cores for the actual streaming (since that is almost entirely dependent on everything but the cpu) and 10 cores focus on bringing you the most crisp and clear image possible.
I think that is where AMD is trying to go with HSA, and if that is the case, I will be buying a future APU when that happens. Am I a fan boy? No. I have an i7 2600k that I just bought a few months ago as an upgrade and I will probably be buying a 2011 haswell e for my next computer (in the far off future since I am seriously broke). That point aside though, if that is the direction AMD will be taking HSA, I want a slice. That seems like that would be something worth buying into, and I feel that is what most people are missing out on.