Improve roadmap visibility of past or future epics
https://gitlab.com/gitlab-org/gitlab-ee/issues/3559 introduces the epics roadmap. Epics with past due dates or future start dates will be shown on the roadmap epics list even though they're not visible on the calendar. When we introduce the closing epics feature, the past due epics can be closed and hidden from the roadmap. Even so, we need to improve the visibility of past or future epics in the epics roadmap calendar, or else users won't be able to see them.
Proposal
The proposal is not ~"UX ready" and needs re-thinking after https://gitlab.com/gitlab-org/gitlab-ee/issues/3559 is implemented