There was probably no incentive to get Vulkan working on VC4, it would have been very hard.
Now the Pi4 is a different animal, with dual 4K screens.
And what little we know suggests the VC5/6 has the extra bits needed?
Once a Vulkan driver is available the Pi4 is then compatible with all those professional level Vulkan tools.
Vulkan on settop boxes etc.
Gaming on settop boxes = gaming on Pi4?
Who knows maybe Broadcom will release a blob
How it will happen and when will it happen, no idea.
But it will happen
Vulkan is available on most platforms now, Pi4 is just one more platform.
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges