Richard Poynder has published "'It Is for Publishers to Provide Plan S-compliant Routes to Publication in Their Journals.': An Interview with Robert-Jan Smits, with Preface" in Open and Shut?.
Here's an excerpt:
That publishers do not like Plan S is, of course, no surprise. That was doubtless what the architects of the initiative anticipated. What they perhaps did not anticipate was that they would face pushback from researchers. Yet just a week after the announcement nine researchers published a critical article entitled, A Response to Plan-S from Academic Researchers: Unethical, Too Risky! This appears to have shocked the Plan S architects as thoroughly as their plan must have shocked publishers.