When I read a book (the paper kind) I detest endnotes, and greatly prefer footnotes instead. The reading experience with endnotes is just too cumbersome.
In some ways, the current setup for looking up footnotes via instant details resembles endnotes rather than footnotes, as I need to manually move the pointer over each footnote marker to read them. And with more scholarly works, with longer footnotes, more often than not the instant detail panel can't display all of the footnotes, unless I keep the instant panels always big, which consumes valuable screen real estate, and makes the instant details panel otherwise unavailable.
I'd love to see tools gain an ability to open its own parallel pane the way biblical texts can open associated cross ref or notes pane that flows with the biblical texts. I'm imagining the footnotes pane that is tied to the tools to flow with the text of the tool, appropriately displaying the footnotes in view. This has the advantage of leaving the instant details for other purposes. For example, as I work with my tagged Greek/Hebrew text, the instant details pane can display parsing/syntax info, while a relevant reference tool can show both its text and footnotes.