Hi,
it's something I have expressed at the last Unite, and they did not seem to understand the benefit of allowing publishers to let their buyers log on with the Unity account, like we can log on with fb or google on various sites.
So please contact Unity and express this, it's important that it's not just publishers that poke Unity for this, but also users.
a Unified account would be so much better ( and it's very easy for them to implement as well...), we don't need to know anything from your account, just your name, email and maybe your license type, the rest isn't needed.
Bye,
Jean