PgCluster, BDR, rubyrep, and Postgres-XL all provide master-master (or analogous) replication schemes. I cannot attest to the robustness / production-readiness of any of them. And yeah, it really is a PITA to set it up with Postgres. I will note that I once[1] lost a whole cluster's data due to a combination of Slony's sharp corners and operational difficulty of Postgres.

The schema visibility thing seems like it might be solvable with row-level security in 9.5? (I.E. apply constraints to the system catalogs, perhaps?)

The UPDATE one is good to know. Did you work around it by doing `SELECT ... ORDER BY id FOR UPDATE`?

[1] - Slony had a problem where global transaction IDs rolling over caused it to do Very Bad Things and we had had to turn vacuuming off because performance during a peak period -- but we forgot to turn it back ON and... So yeah, a combination of sharp corners in Slony and Postgres + user error == our cluster systematically ate itself.