(1) It's a proof of concept, (2) it hasn't been updated in 3 years and (3) it still isn't the same syntax as MongoDB.
The point still remains that PostgreSQL isn't just a 1-1 replacement for MongoDB which is pretty common sense to me anyway.
1) it's a proof of concept that others have improved upon to show that you can indeed replace the functionality of mongo that most developers tend to rely on.
2) neither has mongodb at that level
3) that's correct, you need to actually use the term SELECT when you use the functions
and you are correct, pg is missing the random data loss that comes with mongo. it will never be 1-1 in regards to that.
EDITING TO ADD:
the important part is the note (the bulk of the comment) that I'm updating partial JSONB data on a very regular basis, and do it using PLV8, getting rid of the need for an unreliable database and instead using exactly what this news story is about.