This could be a good architecture choice indeed.

The way Sass plugins are usually built is the following:

```
directory/
directory/mixins/
directory/tests/
directory/_plugin-name.scss // including all the mixins
```

And then you should be able to include the plugin without outputting any code (if you want to use helpers only for example).  
To output code, generally the method is to use mixins.

Should we have a grid system plugin with its own test suite, documentation and a clean separation between the mixins and the code?
That could speed up development and interaction with designers if this "plugin" could evolve outside the app. What do you think?