Adding Vega support to AMDGPU is a big task due to all of the changes over Polaris and other recent GPUs. Vega rolls out a new video BIOS interface, lots of new hardware intellectual property, support for video decode using UVD (UVD 7.0), support for video encode using VCE (VCE 4.0), support for 3D via RadeonSI, power management, full display support using DC, and support for SR-IOV virtualization.
This 40k+ lines of code is on top of the tens of thousands of lines of code needed for DC/DAL. AMDGPU Vega's display support is built on top of DC and thus that will need to land in order to allow this new hardware support to happen.
Seven device PCI IDs are currently listed for Vega. AMD is currently rumored to be launching AMD Radeon RX Vega in late May.
The 100 patches up for review can be found on amd-gfx. I'm still digging through the patches and will update if I find any other interesting remarks. The next opportunity to merge this code will be Linux 4.12, assuming its review goes well and AMDGPU DC gets accepted to mainline.
Update: Patches are now available for the Vega support in Radeon Gallium3D as the main user-space component.