Questions
Should the “skip to content” link be included in an landmark region?
This is up for debate, since landmarks are used to navigate to content, and no one would likely ever need to navigate to this link. If you are using landmarks to navigate, you don’t need “skip to content” link.
Here is a discussion on d.o on the issue: https://www.drupal.org/project/drupal/issues/3098828
The question might be whether we should wrap the link in something, just so it is not flagged by accessibility tools, and if so, what should that landmark be?
Should the “skip to content” link land before or after the breadcrumbs?
This is kinda a subjective issue, since the skip to content link should bypass content that is the same on every page. While some of the breadcrumbs are likely the same on every page, they are partly unique for every page.
There are people on both sides of the debate:
https://stackoverflow.com/questions/54884409/skip-navigation-link-should-anchor-beyond-breadcrumb-or-not