According to a semi-official replay at gpuopen.com site, AMD driver team is working to re-enable asynchronous compute queues on GCN1 GPUs (7700-7900, 280, 370 etc…) under Direct3D 12 (Under Vulkan it works fine).
Here it is the answer of Stephan Hodes: “Please note that I’m not an official AMD spokesperson on this subject, and I should have made clear when posting, that this is only my personal understanding of the situation, which might be wrong or at least contain some invalid assumptions. It appears the official driver team has already issued a statement that they are aware of the issue and currently looking into it”.
Our teammate Alessio has got on AMD's nerves during the latest days, even on official AMD community, but now it seems AMD will solve the problem. Stay tuned: we will report if AMD will have done a good job.