You can apply some of the DIR principles very neatly with a BC and an Air2, although the ensuing setup will not be compatible with either GUE or UTD equipment requirements.
The basic principles is to donate the regulator you are breathing, and you do this because you know it is working properly (and for technical divers, because you know it supplies a gas that is safe to breathe at the depth where you are). Anyone who is using an Air2 for a backup is following this principle, which is great. But if you practice with your setup, you will quickly realize that sharing gas on a 24" primary hose is quite uncomfortable and not very secure -- if either of you has any instability problems on ascent, it will be awfully easy to pull that reg right out of the OOA diver's mouth. That's why "octo" hoses are 36" or 40" long, and your primary hose should be at least that.
The problem is that, when you go to a 36 or 40 inch hose on your primary, you're either stuck with a huge loop sticking out to your side, or if you try to run the hose under your arm, you'll find the regulator won't sit well in your mouth. This can be fixed by adding a 90 degree hose adapter, which makes everything a bit more complicated (and adds an o-ring, which can fail or leak), or by using an even LONGER hose, that you can wrap around your body. A 5' or 7' hose, because it comes around the back of your neck, sits quite nicely in the mouth. I like 5' hoses better for people who are using traditional BCs, because there is no really good way to secure a 7' hose except to tuck the excess in your waistband, and depending on the BC, it may be hard to keep it there. 5' hoses can be a bit short for people with broad torsos.
So yes, I would say there IS a reason for using a wrapped hose, which is that, in addition to giving you even more flexibility and comfort while sharing gas, it is also better streamlined and neater.
