My alma mater (UC Santa Cruz) does exactly this, all course were pass/fail and if you passed you got a narrative evaluation, which ranged from terse sentences t

My alma mater (UC Santa Cruz) does exactly this, all course were pass/fail and if you passed you got a narrative evaluation, which ranged from terse sentences that obviously encoded traditional grades as text ("He did very good on the midterm, and excellent on the final, and excellent overall.") to some that were several paragraphs in length and discussed specific merits of the work done in the course. Amusingly they also had a committee that would translate your narrative evaluations into numeric grades so you could apply to grad schools that required a GPA.