With Jon Tennant, Dmitri Zaitsev and Christian Gogolin I have submitted substantial feedback. The abstract:

We argue that Coalition members should favour, both in words and via their spending decisions, community-controlled, no-author-fee journals over commercially owned journals charging APCs. This is for reasons of fairness, economic efficiency, and sustainability. We see Plan S as a strong statement and step in the right direction, but encourage Coalition members to be more forward-thinking about how they want the future scholarly publishing market to look, and make sure that they are giving due consideration to the non-commercial elements of the ecosystem.