Ability to DELETE (not just hide) resources from library.
Personally, I would like to see a "check-box" in the library window, so that individual resources (or entire volumes) could be "checked" or "unchecked." I envision something like the iTunes main music screen. One could sort their library, "uncheck" resources that are seldom used, deleting them from their hard drive. This could save a great deal of disk space for some users. So long as "only checked resources" sync/update, I think this would be a great feature. To re-download the resource, just re-check the box.
This is what the “hidden resources” feature does; files are deleted from your hard drive when you hide them, and updates for them are no longer downloaded. https://wiki.logos.com/Hiding_Books