Hello,
It seems like the Proxmox Blesta module has been neglected recently and I think it deserves an update. Other billing systems and 3rd party developers have updated their respective Proxmox modules to add support for LXC, drop support for OpenVZ, and add other cool built-in features for the client such as firewall management and backup management. I also think the Proxmox module should be updated to remove the Java VNC console and add support for the HTML5 noVNC console that is packaged with Proxmox.
All of these things have implementations in the Proxmox API so I don't think it would be too difficult.