Without being aware of the undocumented feature of tuple shuffling (let alone it's possible deprecation), my example certainly looks like it is clearly related to that of the OP, so my mentioning of it and your explanation helped the OP, me and other readers of this thread to get a more complete answer to the original question.
I think every Swift user and compiler dev should be concerned about the currently (not future) intended behavior not being documented.
As seen above (and in almost every tuple related thread), it's not only me who is confused.
After years of bumping into and reporting what often turns out to be tuple related bugs, no indication of things getting better / less confused, and no clear acknowledgement from the core team that the currently intended design need to be clearly documented, I've made it a habit of pointing this out.
That said, I will stop if you and a couple of other people more experienced than me tell me to. But I will also not report any more bugs unless I'm able to refer to said documentation.