Hmm, well, she's always been a bit of a contrarian within the art world and as a performance artist there's isn't really anything exclusive to sell that can be devalued.
Clothes, and occasionally the complete lack thereof, have always been pretty central to her performances. 'The Artist is Present' is the one that most springs to mind when it comes to dress as an integral part of the work. I think she was also quite close with Riccardo Tisci, then at Givenchy, at the time, maybe he made the dresses she wore, can't remember (just remember the dresses being great). And I think there was also some sort of odd ball collaboration with Jay-Z at some point. So it's not totally out of character, just a bit more down market?
Anyhow, I'm still not convinced it's a clothing collection. Cos used to comission an abstract stand design by an architect or designer annually for the Milan fair (I think covid killed them), it was just part of larger brand building. I suspect it'll be something similar to that, actually a sponsorship but framed as a Collab to help the brand move away from its traditional classic roots into this quasi intellectual minimalist thing they've been morphing into.