Thanks for the detailed response. I'm curious, is the NoSQL store a canonical store of its own data? If not, how do you replicate from postgres to the secondary store?
I ask because where I work we sync postgres to a secondary store for search, but the way it's done in a piecemeal, application-specific way gives me the heebie jeebies. It almost certainly will result in that secondary store drifting. Unfortunately we can't use something like zombodb [1] as we're on amazon RDS. It seems like you know your stuff, and seeing non-deterministic consistency irritates the heck out of me!