I do not like that you expect redundant fields be omitted. Just because they might be the default does not mean you shouldn't show your business rules
The following implies that bar might be null-able if you don't know what the default is.
foo = text(null=False)
bar = text()
It's "have you considered" rather than "you must do this".
The dev has the choice of if to commit the change that is suggested
That gets a bit lost in the game I know :)
To me the benefit of the default redundant arguments error is pedagogical. It forces me to think more closely about what it means to set nullable, assuming I was coming to the game with a limited understanding of Django code. Just glimpsing a note in the docs doesn't register nearly as quickly interactive play does.
I would love to see this format used more extensively. When I'm learning an API I tend to fire up a REPL and explore it by poking. I do it even with basic mathematics that have fallen out of my brain.
Very much enjoyed and it served as a quick refresher!