This is a really interesting thread ... will be doing my DP next year in SM so really enjoying the interactions here.I'm going to have to ask my instructor how he prefers to do the regulator swap. GUE prefers right hand right regulator, left hand left regulator. A TDI DP video showed swapping both regulators using only one hand. I practiced both ways.
My two cents on the above is that you should practice reg swapping with one hand... If you intend on going down the cave / advanced wreck route you will almost always have your light on your left hand and need to keep that steady, therefore using right hand only to swap regs, clip off, etc is something you will need to drill.