[necovek]

Wouldn't it be easy to migrate a NoSQL database to Postgres without any adaptation?

Postgres is an "object database", so you could use Array, JSON or JSONB fields wherever necessary, and you shouldn't introduce any foreign key relations or such.

[xyzeva]

It would, except if you have a f'ed up schema like most of these companies had.

[marcosdumay]

The point is that Postgres has no problem at all with a fucked-up schema. You just tell it not to check a thing, and it won't check a thing.

But then, I may be underestimating how fucked-up things are.