Is there any value in keeping the kernel closed source ?
It prevents forking. MS doesn't want to compete against its own kernel. Even Android doesn't want to compete against itself, hence the manufacturer agreement(s) that make it effectively closed.
yes I agree, as a corporate entity this has value. But by being closer to the unix based variants they would be closer to everyone else to port cool things over and to use innovations via osmosis. Android is effectively a unix variant. OSX etc. They all benefit from the unix/linux/bsd ecosystem.
It prevents forking. MS doesn't want to compete against its own kernel. Even Android doesn't want to compete against itself, hence the manufacturer agreement(s) that make it effectively closed.