If I'm looking at an epic, one of the things I often want to do is look at all the issues in the epic in the issue navigator and then filter on them.

For example, today I wanted to check that none of the issues in my epic are in the "Needs Triage" state, that stops them being on the rapid board we use. I spent way too long trying to figure out how to do this without going to the issue navigator and then using JQL.

I think an appropriate place for this would be the little dropdown that you get for Sub-Tasks. I know that epics don't currently have that dropdown, but obviously they should. An issue with a collection of issues in it should probably list the issues the same way by default. I can't immediately think why the sub-task list should contain "Show All" and "Show Open" menu options but the "Issues in Epic list shouldn't". My guess is just different developers.