Thank you for your post. What you’ve outlined will likely involve extensive code changes to the OJS code base and/or plugin development. As a starting point, I would invite you to have a look at our technical documentation, to get a better sense of what’s involved and how the software development process works: https://docs.pkp.sfu.ca/dev/
If you or your client would like to make specific feature requests, I would invite you to create post to the feature requests category here on the forum (please list each separately and follow the provided template)
This is not quite what you are looking for but does relate - we are working on some developments around JATS XML for the next iteration of OJS.