It would be helpful to quickly see what to focus on at a glance from the BIS list without having to hover over each item for its source. For example, list M+ dungeons and raids source for your missing BIS items in a table on the side (2 items form X, 1 from X, 1 from X, etc.)
We are working on some new features related to Best in Slot and the Upgrade Finder in general that I think will be convenient for BiS-focused players. We are hoping to do a beta sometime around the next season’s release.