the vanilla theme is a "Learn how to do all the things in Drupal8" with a theme that dont have any flavour, that sound fancy, in reality its a collection of documentation and theming best practices, where I try to navigate away from the last Drupalism's that still exist.
All development are dont on github, cause honestly drupal's patches is harder to get into, and i hope to get more frontender involved, also i like PR's more than patch files.
But all issues & releases will be done on d.o