One possibility is to use a tool like MyST Markdown, which can export to many different LaTeX templates, or create a website.

https://myst-tools.org/docs/mystjs/creating-pdf-documents

Then the switching of templates actually is one line. There is also hope to get a bit further in the publishers system (which ultimately needs JATS XML), because MyST can also export to JATS (which is used for pubmed etc.).