I am going to be teaching tourists how to sidemount for travel, and the thing I have basically worked out is that while Air2's might be of various usefulness for regular divers they make sidemount diving very flexible. (And for travel flexible helps fit to what is avaiable.)
The problem with a single sidemount/double sidemount switch out can be that you either have an extra reg or no octo, or you have to use tools to switch between the two. Going with a multipurpose harness, and leaving the inflator in the standard backmount location with an Air2 on it means that the left reg can be used as a single BM, single sidemount (on the left), or as the left side in double sidemount.
Interesting suggestion
beanojones, I didn't want to mess with my setup constantly going from single to double and vice versa. But trying to source Air2 mod on a non Scubapro BC could be difficult?