I noticed that in repository admin and repository view default privileges showed the repository field non-grey so appeared editable on the quick.
More careful inspection reveals that the field is a dropdown and interaction with it is not possible, however, it still does not have the same treatment as the other non-editable fields.
Field of the same type (dropdown) appears as non-editable in repository (in the blobstore field) once you create the repository, so I do believe this is possible to fix.
I did not check older NX3 or NX2 at this time. Debug was off for this test.