There is no turn in the feather step because there is no change of direction of progression. CBM does not require the track across the floor or the feet to turn - it's purely a change in the angle of the hips and body relative the to feet and motion. In the case of the feather, the motion is across the feet at a shallow angle for all three steps. Yes, you can do a version with turn, but it's not the version described in the book.
For outside partner steps, yes you could unwind the body a bit before taking them, but your momentum would still be aimed at CBMP, thus the positin is already predesitined and not a result of CBM on the step itself. Getting a full swing in this situation is a matter of learning to swing straighter than many do for an inside partner action - master this and you will also be able to have a nice big swing from the almost-CBMP position that the British teach but you don't like on step 1 of an inside action.
Most people do not achieve CBMP in a spin turn, however they may in a pivot turn. In the pivot turn, CBMP comes from the placement of the first step on the track or the standing leg, as set up by the rotation between 2-3 of the previous figure. What's important here is not that step one is in CBMP (that's obvious, though many place the step incorrectly) but ratehr that this across the body position is to be held through the pivot. Which is again something that many fail to do, especially on repeating pivots.
Perhaps another way of saying it is that except for outside partner, there's nothing "mandatory" about CBMP. It's just a name for a position you will sometimes find yourself in if you dance in the style described in the book. If you modify things (as many do today) you won't necessarily have book CBMP in all the positions the book suggests you would.
