In an era of quiet luxury on one end and streetwear on the other, YSL has somewhat of a monopoly of that glossy, cinematic image, so I don't think they should move too far from that look. What they really need is to take a more grounded approach to the actual design, take a page out of Pilati's book and start thinking about what his YSL woman could wear before 5pm.
Let's take the latest collection as an example. The suits at the beginning of the collection could've been diversified by adding slimmer cuts, switching the pants for shorts and skirts, adding waistcoats. The "gypsy" looks in the middle could've been styled with cargo shorts instead to those sweeping skirts. The colourful looks at the end could've featured one-piece dresses, shorts, pants, a different jacket shape, etc.