Requests for comment/A central repository for templates and other bits and pieces

Background
Other MW wikis templates are either written from scratch or exported from Wikipedia.

Problem

 * Non-WMF wiki administrators are having to debug templates, and struggle to keep them up to date.
 * Wikis may include Wikipedia specific features and images.

Proposal
There should be a common repository for templates and other bits and pieces, e.g. CSS and JavaScript.