Yeah good luck getting a company to give you VPN access to their network without demanding you've been keeping your operating system patched. BYOD without such policies is a great way to make the network support staff quit and maybe slash your tires on the way through the parking lot.

It's called _attestation_ and Windows has been doing it for some time now with VPNs and domain credentials. Attestation actually makes it possible for BYOD to be done in a way that's not going to simply repeatedly expose one's network to every kind of malware known to man.