People do so much hacking and such on things like the Billy bookcase. They'd be just better off getting the plywood and building the carcass themselves, and it'd be 10x more durable than the ikea cardboard version. I've watched several videos of people spending multiple weekends turning them into built-ins....and then at the end of the day, it's still a cheap ikea, cardboard shelf, that will bow under weight, etc....