Yes, the DP (data plane) in the demo acts as reverse proxy, it routes the downstream http request to the upstream according to the configuration. The CP (control plane) just translates the json configuration to sql and get it executed in the postgresql.
Yes, it does so in our company. The etcd is somehow heavyweight to be the configuration center. And event more, the postgresql could be deployed in de-centralized cluster just like what etcd does, via some tools (e.g. raft-based failover agents) and configurations (I helped my customers to achieve this goal, but the solution is not open source yet).
Is it stretching the definitions of data-plane and control-plane? Data-plane is the reverse proxy users interact with.. maybe it does make sense.