It’s always nice to see such efforts around Postgres. I do think it’s very well suited to many needs aside from extreme scales that most won’t deal with.

In terms of graphs, there is also an implementation of Tinkerpop which allows using Gremlin, very different in nature to Cypher.

http://www.sqlg.org/docs/2.0.1/

NB: I believe cypher can compile to bytecode that runs on the tinkerpop engine which I found interesting