I'd certainly would miss OpenVZ. I've got quite a few machines running on it. It's super fast to set up, and simple to manage. I love it.
That said, should it be determined that it needs to go, please at least provide some "streamlined" way of migrating OpenVZ to KVM machines. Reading through this thread, a lot of people, just like me, have a lot of OpenVZ machines running on PVE. I don't even want to think about the time sink it would mean, migrating all the OpenVZ machines to KVM.
I must say, if needed and possible, I like the idea of two versions. Install OpenVZ or KVM. Then, keep the management interface, allowing admins to manage all their PVE hosts in a cluster, OpenVZ or KVM, from the master machine.