I love how discussions about coding style could go virtually on forever :smiley:, as said it's unimportant and I'll stop here but just to clarify:

* when referring to the PHP manual I wasn't mentioning the examples but this:"Having a trailing comma after the last defined array entry, while *unusual*, is a valid syntax" (as it would be, just for the fun, triple wrapping boolean expressions, e.g. (((1===1))) )
* I'm not familiar with Zend's, Symphony's or any other than MediaWiki's standards, which don't list it in the recommendations and are what we adopt
* the bulk of the trailing commas are in language files, in the extensions folder and in our code (as in wikia subfolders), it's inconsistently and sporadically used in core
* I consider better not to make it an habit when working in different languages as it has different meanings/effects (and their linters)