Agreed. This looks rather dire though, and it sounds like given the work that would be required to move to Vulkan and then adopt adopt MoltenVK that Blender might just not be able to work for a while once OpenGL disappears 
EDIT - It seems like Apple keeps various depreciated APIs around for a long time on macOS, so i’m hopeful that it only disappears when Blender is finally able to adopt Vulkan.