Views relationship to more easily display multiple levels of child entities

As requested I'm making a separate issue from #2550957: How can I create a view of all groups

The problem is that in a view you can't easily display child entities that are more then one level below a parent entity. The relationships are currently focused on maintaining the hierarchy built into the system but sometimes you just want to ignore that organization and display everything.

A simple example is if you want to display all subgroups of a certain type no matter how deep they are from the parent. Another is if you have a parent group with article nodes and you have subgroups with article nodes you can't easily take the parent GID and display all article nodes for both the parent and subgroups.

If it is possible to add a way to control how many levels to include, if the parent group should be included, and group types to include(possibly could be handled by default views filtering?) that would make it really easy to get results that are somewhere between what we have now and just getting all the things.