Slim I would say
Stages can already feel pretty cramped to be honest, and the layout would have to become somewhat nonsensical to get thinner. Because of the grouping behavior of Stages, the spatial arrangement is pretty essential. I suppose I could see shaving off 2hp by doing a segment/2ph, but it would be super tight then.
I agree with @Jay: if I could make one change to the layout, it would be longer sliders. Oh, maybe bigger staggered clickable rgb knobs to make them a little more playable at the same time.