[tracking] upcoming major versions of mjml (JS)

[FelixSchwarz]

It seems like new major versions are more about internal refactorings and replacing "add-on" components like the minifier or the beautifier rather than additions to the core mjml syntax. Still this issue can be used to gather notes:

• Roadmap v5
• MJML6 Migrate from Lerna to NX, and introducing Typescript

Overall verdict of the main upstream developer about the code quality (1):

I don't know if anyone will read this but given the time I have it's hard to find time to add new features into the codebase our test coverage purely sucks, releasing new version sucks, installing the project locally sucks.