exactly. Students are people with lived experiences and expectations that drive how they perceive things. A lot of times things that are 'theoretically' better in education bomb in practice because they conflict with students' emotional/psychological needs, wants, and expectations. There are NORMS and all this does is mess with the norms the faculty can control - but not all the norms. The most important thing he is doing is cleaving formative from summative feedback.
This isn't really a perfect with the underlying principles of ungrading...this isjust ungrading within the controlled climate of the course itself. Thats great, but the problem is his drive towards formative feedback over summative feedback is constrained by outside forces. There is still a grade at the end of the course and that makes it hard. And then add in that if too many students do well you get accused of 'grade inflation' (which is a whole nother ball of nonsense). Students KNOW there will be a grade at the end, to act as if there isn't is just introducing ambiguity not necessarily learning. You can bypass some of the problems with strong trust - but only some. Specific to the comment on rubrics, GOOD rubrics can't really be useful, self and peer evaluation can be useful, using the rubric to provide formative feedback can be useful. Revisions can be ESPECIALLY useful. But you can't truly (ugh...sorry, no true scotsman) within a typical university that demands I assign grades. Anything you do to try will be 'gamed' so the best you can do is make 'gaming the system' and 'learning' as similar as possible.
I would love LOVE to just have all of the classes I teach be taken as pass/fail but they aren't and can't be based on the external systematic rules. I've settled on a tool called 'specifications grading' as a middle ground that basically translates learning behaviors and outcomes into a clear grading system.