@ProfKinyon
Thank you for letting the community know this story. This reminds me of the same action done by the journal of machine learning when 40 editorial board members resigned in 2001 and created the fully open JMLR
https://en.wikipedia.org/wiki/Journal_of_Machine_Learning_Research

Do you consider moving your journal to another place? For instance, the open and non-commercial episcience initiative already hosts several mathematical journals? https://www.episciences.org/publishing-model/
https://www.episciences.org/journals/?cat=2232