I found a last-minute bug related to xorg-server building with some new tweaks to mesa and libglvnd. I have applied some fixes and as of right now the tree is being regenerated. When you have the fixes, 'glvnd' global USE will be enabled with workstation or desktop profile. And you may need to re-emerge mesa-19.1 if xorg-server doesn't build. Since it's a beta, I won't always make things perfectly smooth -- that is the goal for the release ?