Content seems to be more important atm. Mac stated that maintaining different versions for Linux and Mac takes up resources because they can’t just build hit a build for Linux button. Eventhough it might not be that hard to enable OpenGL or Vulkan support (unless some custom shaders start complaining). They made their own modifications to UE4’s source code so they have to port them over as well.
An example for this is the Linux DS server. When they launched TU it would crash about every hour while the Windows version was much more stable. Eventually they fixed all these issues but it took them some time.
But don’t worry they’ll get back to that eventually as they promised Linux and Mac support on their Indiego campaign.
EDIT:
Here’s probably your answer: