I'm not a OS Programmer, I'm afraid - embedded and scientific applications is where I direct my programming. However, I don't understand what about Windows (and macOS/iOS) oblige Evernote itself to be open. I've had a very quick browse of the EN API (https://dev.evernote.com/doc/articles/data_structure.php) and, on the face of it, it seems doable.
Why can't a macOS menubar item and Windows equivalent, for example, login in to a user account and interface with the Evernote database to, say, insert a (automatically time-dated, located) note into a specific Journal Notebook. Ideally, I'd like Evernote to insert each new entry into a single (auto-created) daily Note. Alternatively, as with Day One, have a display that groups and sorts the Notes for each day (perhaps using the same method that EN uses to display Stacks, eg set the stack field to the Notes "journal" day?).