our pmxcfs is not compatible with opennode, and yes, we do not use libvirt. vzmigrate is only for OpenVZ. our system is based on corosync, so there are strict rules for cluster members - a opennode server can never join a proxmox clusters.
beside technical issues, what is the benefit of such a feature? for me its just 100 % useless, means I would never use it and also other think like this. are you willing to pay Proxmox and Opennode dev´s to work on this? I am 100 % sure no one will finance this.