The idea of selling the off-shoot products of fashion is nothing new. The designer selling an audience the essence of a fashion collection in the form of a perfume, watch or pair of sunglasses is arguably a way to make the brand inclusive, ensuring that anyone can feel part of the designer's world, even if they can't afford to wear a catwalk-ready ensemble.
The idea of sharing a part of a designer's world through a different medium, even if those items are outsourced to another designer, is also just a logical progression of design process: If you design clothes, at some point you are going to wonder what scent matches the ensemble, what kind of sofa its wearer would sit on, and so on. Next thing you know, there are Chrome Heart's branded hand saws and Supreme branded crowbars.
Of course there may be gimmicks along the way; but overall, if designers design, then why not let them spread their wings?