Jedibeeftrix

Vulkan is the only future. OpenGL drivers are going to get less and less attention from Intel, AMD and nVidia going forward. So unless the hope is to run TDM over an OpenGL > Vulkan wrapper then it gets increasingly hard to see how any Intel Skylake and higher, AMD GCN 3rd and higher, Nvidia Kepler and higher get to play TDM (which is perhaps a perfectly valid strategy). And if this is the strategy, then it's far enough in the future before OpenGL driver updates stagnate that it doesn't need to be worried about yet.

is that other IDTech4 branch Vulkan only, or does it maintain OpenGL in addition to Vulkan?

Is there still a possibility of moving TDM to that other branch of IDtech4 which has a vulkan renderer - without it being too disruptive to the tooling, assets and investment that has been put in the version we have now? It does seem for the long term support of the project that vulkan is the way forward.