Many of the people working on RADV are already employed by AMD (or paid by them indirectly), so arguably it's already collaborating.
I see the amdvlk/radv drivers a bit like the windows "Radeon Pro"/"Adrenalin" driver split, one is for people who stare at solidworks all day, the other for everyone else.
I think AMD wanted to phase out that distinction for OpenGL for example, so why wouldn't they want the same for Vulkan There is no need for them to be different really in that sense.
amdvlk and radv exist for historic reasons since they started independently and amdvlk was designed to support Windows too. But today I don't really see a big point in admvlk except where radv doesn't exist.
So AMD can do what Intel does. Support radv on Linux and amdvlk on Windows for example, or as above, try to make radv work on Windows too.
I see the amdvlk/radv drivers a bit like the windows "Radeon Pro"/"Adrenalin" driver split, one is for people who stare at solidworks all day, the other for everyone else.