Emily Farrell, in a Scholarly Kitchen post:

Monographs, by their nature as specialized texts, often see low usage. Scholarly publishers are aware that in order to support a diverse program of scholarship, it can be necessary to subsidize, in part, long-form works that have a narrow audience. Other, more equitable models are emerging to support open book publishing. There are fully open access presses, like University College London Press and Athabasca Press, that are thriving using an institutionally supported model to support mission-driven monographs publishing. There are increasing numbers of scholar-led and university owned publishers, many of which are open access. There are new cooperative models for books that, like [MIT's] D2O, forge a more cooperative pathway for monographs. Opening the Future, currently in implementation with Central European University Press, is another example of an approach that builds a community around scholarly books publishing. All of these models are looking towards more collaborative, equitable, and accessible ways to open books for authors and readers while maintaining financial sustainability.

It's a good piece, but weirdly silent on the 800-pound rival to the surveyed models: the book processing charge (BPC). It's hard to argue for an alternative to the author-excluding BPC without confronting its existing foothold.