patroni builds upon etcd and (optionally) haproxy, two rather mature pieces of infrastructure (which can both be made HA on their own if SPOFs are to be avoided).

I understand where you are coming from, but having this kind of multi-server-who-is-master knowledge baked into Postgres itself will surely take another couple of releases, if it will be included at all.

Probably BDR (bi-directional replication, master-master like logical replication) will be there first, but whether the question is whether it will help a lot for local scale-out workloads (as opposed to glueing two datacenters together and allow transactions on both sides).