I'd really like to be able to customize the sorting of the books in my TBR. Right now they just display in the order they were added, most recent first, but this is not always reflective of the priority I actually want to read things. Having five "up next" slots is nice, but ultimately pretty short. Ideally I'd love to be able to sort my TBR into multiple groups or shelves (I currently use tags but it's a non-ideal solution) and then be able to order them by priority within that group. That'd make it much easier to find the next book I want to read.