Hello,
Upon reading these articles
https://dev.to/maxlaboisson/an-introduction-to-api-first-cms-with-directus-open-source-headless-cms-9f6
https://snipcart.com/blog/jamstack-clients-static-site-cms
I was thinking that PW can be used for a Jamstack or Headless CMS with no changes at all.
You can easily create REST Api with PW or use the GraphQL module
https://github.com/dadish/ProcessGraphQL
So ProcessWire is an Open Source Headless CMS since 2010