I was doing an onsite with a client earlier this week, assisting in a demo of the Drupal 8 solution we were building for their team.
In my last post, I detailed how you can add new repository endpoints in your composer.json file for your own repos.
On a recent project, we had taken a Pattern Lab based prototype and created a Drupal 8 theme from it. In order to track updates and stay independent of the work happening by the front end team, I added the Pattern Lab repo to the project as a git submodule.
In Drupal, most breadcrumb generation and navigation is sufficient by basing it off of the menu hierarchy with the Menu Breadcrumb module.