The extension isn't just a Javascript overlay, it actually modifies the document in real-time while storing a full understanding of the document structure behind the scene, in the document itself (thanks to the Google Docs API). So other users would see "=name is out!" if this is what you've chosen to show on your own interface, or "MySoft 1.0 beta is out!" otherwise. If they have installed the extension, they would be able to access the document structure information, see placeholders and change variables as they like.

This extension stores all formulas as named ranges inside the doc. Because all changes are simultaneously visible by all users, including computing and revealing formulas, it depends on what users with the extension are doing.

This also means that users without the extension can modify any revealed formulas or definitions, and have users with the extension recompute them.