Following the previous blog and some investigation, it turned out the kernel package from Mystro256 COPR repository based on agd5f kernel branch (one of AMD developers) resolves the blank screen issue. That could trigger a problem for users having a new AMD graphic hardware so perhaps a warning should be written on the release. Perhaps having one of contributors be part of kernel team bringing these improvement until those patches arrive to the mainline kernel for a better user experience.
Past the issue, the desktop experience with Radeon RX 560 was tremendously improved compared to the retired GTX 460 v2. Gnome on Wayland on Fedora runs smooth showing how far the open source amdgpu driver went through compared to previous years. That was also the opportunity to run a vulkan based smoke test demo on RADV, which is a counterpart of glxgears.
Overall the card is excellent once missing software are installed.
Running Fedora 28 Design Suite post beta shows a nice surprise: Vulkan with RADV is fully functional on both South Island (Hainan) and Sea Island (Kaveri) cards on ASUS X550ZE laptop. amdgpu driver is needed to enable the feat in combination of boot parameter (cik.amdgpu_support=1 cik.radeon_support=0 si.amdgpu_support=1 si.radeon_support=0)
Some minor issues need be to addressed like occasional glitches. Otherwise the performance is stable enough for dail use.