That isn’t in-place, but IIRC, I believe we are moving away from creating mutating/non-mutating versions of every operation, in favour of optimisations that will reuse existing storage when it is able to do so.
I don’t think that’s been implemented yet, and personally I’m sceptical, but I believe I remember some of the Apple engineers mentioning it and they seem to believe it can be done, so... we’ll see. It would be extremely cool if it worked.