Work sessions are for Neutron contributors to discuss implementation details and making quick progress over specific issues, in a small work group environment.
The FWaaS project was marked experimental in Kilo for the third consecutive release. Meanwhile, it's overlap with SG is obvious. We'll decide what to do with FWaaS here and how we can morph SGs to cover any use case FWaaS is letting us have right now which SGs don't currently cover.
