Myself and a few others in the Contrail team have been working on a cloudstack network plugin that interfaces with the contrail VNC (http://www.opencontrail.org). At the moment the plugin provides isolated guest networks (and a virtualized "Public" network) as an overlay that is capable of interconnecting directly with routers/switches that implement the existing standard for network virtualization (RFC 4364).
We would like to contribute this code to CloudStack. We intend to continue to enhance it in order to add full support for functionality one would expect out of the EC2 VPN API. What is the process to do that ? thanks, Pedro.