I would add here that I also dive with different gear configurations based upon the dive. I mostly use my doubles with my dry suit and therefore have a redundant supply and simplified equipment. With students I always begin the class with whatever their gear configuration is, most often a jacketed BCD. I normally change to a BP/W with little weight other than on the backplate. Again depending on the class it may of may not involve a pony but it provides others an opportunity to experience diving with someone that has another gear configuration different from what they may have. As far as rescue with a BP/W you just have to become familiar with the different equipment to become comfortable with handling any situation. When it happens for real looking back on what you learned will provide the needed foundation, another reason to introduce different equipment configurations that one may encounter in a rescue class.
While I have used and taught a few students with Air2 I do not own one. As for myself I normally hand off my primary and have my backup on a necklace.
Great discussion and thoughts but your right ya gotta put these into practice until they are second nature and good communication between you and your dive buddy is the #1 thing that can prevent a problem. I for one will admit to having been to complaisant in the past but a good dive buddy brought me back around.
Best Fishes!! [