> All of that said, I work in an innovation space where we throw a lot of things at the wall to see what sticks, and our time-to-prototype is often a few months at most. For us, it has been a godsend, but our situation is rather unique.

The very RAD reasons you note regarding Mongo also encourage Mongo Cancer (tm).

What is Mongo Cancer you ask? It is the phenomena where Mongo use is manifest from API to home-grown "relational logic" in business tier. This simply doesn't happen with any other NoSQL DB afaik, but Mongo Cancer uniquely marches right up to the user's face in the API.

> I think if you have separated your concerns well-enough, it is okay developing in Mongo while leaving yourself a path to postgresql or something else.

I'll hold you to that "I think" and assume you have never actually done this.

Because Mongo Cancer patients typically love the RAD aspect of grabing JSON hot off the http stack and shoving it in the "database", touching every API in the way. The last M.C. project I saw required effectively a rebuild to actually swap the misused Mongo.

tldr; Mongo Cancer is very easy to catch but requires very expensive surgery to cure.