I can't really see this changing until the new API's become the norm and DX12 and Vulkan are available from release on new titles rather then patched in latter down the road.
AMD hasn't forgotten DX11, and in fact spent a long time recommending it for devs who don't want to hit the metal with a lower level API like Vulkan/DX12. AMD hasn't forgotten that there are a lot of DX11 games and will be for some time.
The utilization improvements are not just to benefit DX12, but to ensure that the Vega hardware itself is better at not bottlenecking regardless of what workloads it is running. This in itself should make the hardware more efficient regardless of whether it's running DX11 or more up to date APIs.
One of the reasons that AMD is partnering with the likes of Epic and Bethseda on the low level engineering of their engines is to get exactly the sort of support you are talking about built right into the middleware, on top of the architechtural improvements in the hardware and drivers.