I think most X->Y procedures in Scheme returns a freshly
allocated Y, and I'm afraid that queue->list and list->queue's
semantics of sharing the storage can lead confusion.

Can they be named so that it indicates sharing semantics?
I haven't come up good names, but just an idea:

  queue-list instead of queue->list

    Indicates that it's an accessor to the internal storage
    ('list' slot of 'queue' record),
    instead of type conversion function.

  make-queue-with-list instead of list->queue

    It's a constructor with special initial value.

If we have queue->list and list->queue, I'd like them to copy the
storage, even if those can be trivial to implement:

   (define (queue->list q) (queue-list (queue-copy q)))
   (define (list->queue l) (apply queue l))

On a side note, don't we want dequeue-all! operation? SLIB and
Gauche has it; for the name consistency, we can name it like
queue-remove-all! or something.