1.0 would be the version where all basic features are present and codebase is clean enough to allow growing more features of different kinds: systems, formats, validations, glossaries, ...
There is no need to have a complete set of supported use cases, but there must be at least enough work on these different domains, and code base must be clean enough that adding more of these is easy enough.
The application should also be mature by 1.0 in terms of stability. As many bugs as possible must be eliminated.
As a requirement, every issue with the
feature label must be closed at the time of the release. New features will then target 2.0.