Plugin Integration with the admin plugin

I recently spent some time writing plugins that integrated with grav-core and the admin plugin. I found it really frustrating that the admin plugin hijacked many services and deviated from the general architecture. In particular:

  1. Pages under plugin/admin/pages do not get put into folders like pages in user/pages

  2. Additional (generic) events are fired by admin and seem to be better located in core. (such as onPageNotFound and onAdminTwigTemplatePaths)

  3. Multiple forms defined front-matter pages under /admin/pages are not recognized.

So I fixed or worked around these issues, and now raise this design question up for discussion:

There are circular dependencies between admin and grav core. How does everyone feel about the dependency issue? Should it be refactored?

If I spend time migrating my fixes for a PR, should they be in admin, or grav-core?