Baptiste presented a talk for this at the Vancouver summit last week which clearly lays out the evolution of this, I'd recommend watching the video when it is published, titled:

Scaling bare-metal network reconfiguration for a large-scale research infrastructure: a journey with Neutron and Networking-Generic-Switch

Hello,

We have been hitting performance issues with networking-generic-switch
(NGS), the Neutron ML2 plugin that performs dynamic reconfiguration of
physical switches, most notably used by Ironic.

In our quest to improve NGS performance, we have designed and implemented
an agent-based system for NGS, and we would now like to upstream it.

Since this is a fairly big change, and some parts of the design such as HA
are not completely clear yet, feel free to join the discussion on the RFE:

  https://bugs.launchpad.net/networking-generic-switch/+bug/2024385

Regards,
Baptiste