I've read some of the conversation which has taken place over the years regarding handling duplicate items, and I think a toggle of this nature would be beneficial to people trying to knock out their backlog. It wouldn't combine duplicates into a single item, but would rather just simply prevent duplicate items from populating only if one copy of the game has some kind of completion on record. This would make the backlog a whole lot more concise without requiring any workarounds on the user's end (such as outright hiding duplicates from the collection on a constant basis, which would not be ideal for a number of reasons).