The Fair Open Access Alliance has released extensive recommendations on the implementation of Plan S. They call for clarifying terminology, for support of no-fee Open Access initiatives, and for making any new infrastructure public and open. Perhaps the most important recommendation is to build cost transparency into the capped publication fee.
Read more: https://www.fairopenaccess.org/2018/10/21/foaa-recommendations-on-the-implementation-of-plan-s/
Meanwhile, Elsevier started a gold OA clone of their subscription journal Water Research (0043-1354) under the name Water Research X (2589-9147). Interestingly enough, the FOAA recommendations already foresaw such tactics and argue that a careful definition of ‘hybrid’ should prevent the Plan S compliancy of such journals.