Placing template styles and documentation on its own namespace

To have templates more manageable and maintainable, Wikipedia has documentation of templates on a separate page. They're in the /doc subpage of the template. In a similar way, with the introduction of Extension:TemplateStyles to move styles outside of the template logic/markup, styles are put also on a subpage of the template, called /styles.css.

However, there may be another approach: Instead of putting them inside a subpage, they could be put on a specific namespace. Because, well, those subpages are not templates.

This discussion may get moot when Multi-Content Revisions can be used to host documentation and/or template styles inside the same template but on different slots.

Implementation
Define the namespaces in LocalSettings.php (they can be named however you like):

You may also want to tune to use the same policy as the Template: namespace.

If you have Extension:TemplateData, it doesn't support other namespaces. You'll have to add this snippet to MediaWiki:Common.js:

Comparison
Let's see a list of benefits/disadvantages of each approach.