They could, of course, but even a stuff pack cannot focus exclusively on cosmetics for CAS. Even Moschino could not.
Shoes could be the bulk, but it would definitely need more athletic wear or something. Plus BB and something that is gameplay, though I am not sure what you could necessarily do that would not feel like Fitness Stuff 2.0.
Even if you consider them possibly debuting a lifestyle as the gameplay mechanic, energetic and adrenaline seeker are already to be had. Same for an active trait.
As for BB/gameplay, the smoothie maker for a healthy lifestyle sort of SP has been suggested before, but I am not 100% a brand would necessarily want to be connected/expressed with that. Speaking of the brands agreeing, I doubt they would want to be stuck together, so we would probably get one brand or a few related ones.
This being said, Athletic outfits tend to be some of my weakest in general and I do agree we need more shoes, so as unexciting as a branded shoe pack would be for me I recognize it as a weakness that needs addressing. I nearly exclusively use the Fitness SP stuff there and relying on one pack is... Limiting.