Allthough some may argue async compute is not a part of directx12 (now), It will be (and sort of already is) for sure. The whole thing is that for gcn GPUs async compute is what makes them shine.
Here is a more detailed explanation. Note that Pascal is not listed and of course, pascal has a lot of touted improvements when it comes to dx12.
But it will help with explaining.
http://www.anandtech.com/show/9124/amd-dives-deep-on-asynchronous-shading
As a side note :
Now the upcoming PS4 and the xbox updates, and polaris for the pc, are all touted for Virtual Reality : VR.
But what i am 99% sure of is that they also will have in common is a similar ace/hws setup. This makes it for game engine developers much easier to port their games from one platform to another. Reducing development and porting costs, increasing the size of the customer base and as a side effect, will make gcn an industry standard for the upcoming years.
The thing is with virtual reality, that for a full immersion, a fluid image alone is not enough. Accompanying audio is also very important for the VR experience.
And that is what gcn is good at, processing data, if that may be video graphics or audio( or even ethereum mining data). Now if you can process both on the same device, it is for the software developer easier to make a prediction how the software is going to perform. I think the reason to do so makes the development of a 3d engine much easier.
I should note that pascal has of course also the ability to process audio and video.