Just got off a call with the editor-in-chief of a journal that moved from paywall-based publishing with Cambridge University Press to university-hosted independent publishing under a diamond OA model (no APCs) with PKP/OJS.
TL;DR it's going great.
Submissions are up, quality has been maintained, and now over 50% of papers have one or more Global South-based authors (previously ~10%). @OpenAlex data]
The European Mathmatical Society, working with research libraries, have found a way to make ALL of the research journals they publish open access, without the need for author-side fees (no APCs!). Bravo @EuroMathSoc