I've noticed various issues with the Boilerplate. For instance, ideally it should come packaged with a Gruntfile and PHPUnit/QUnit testing framework in place to make development easier. Keen to work on this but would like to manage these sort of tasks in Phabricator.
Topic on Extension talk:BoilerPlate/Flow
The tasks and bugs for this and Extension:Example are in Phabricator, project/tag #MediaWiki-extensions-Examples.
BoilerPlate now comes with a Gruntfile.js and has the standard npm test and composer test Continuous integration/Entry points. No actual PHPUnit, QUnit, or browser tests (phab:T108108) yet, patches welcome.