The greatest thing about all the refactoring in Drupal 8 is that, in general, a lot of those special Drupalisms used nowhere else were thrown out and replaced by sound design patterns, industry best practices and concepts that newcomers from other branches of programming will have an easy time of recognizing and using.
But, of course, this has already been discussed in a lot of other blog posts, podcasts, sessions, etc., by a lot of other people.
What I want to discuss today is one of the few instances where it seems this principle was violated and a new Drupalism, not known anywhere else, introduced: plugin derivatives.