This basically takes advantage of the 3 seconds you have to put your dots on a new target.
I actually figured this out after I put this video up, but, I'm pretty sure the most optimal strategy is Inhale > Haunt > Exhale when you have shards and Inhale > FF > Exhale when you do not, that gives you time for a haunt, uses the full 3 sec you have for soul swap which will extend dots even longer and gives you no downtime. With how weak MG is I can't see this being a loss. You also need to figure in the time NOT spent recasting dots.
You need to make sure Agony is at 10 stacks, which happens very quickly on a normal opener. I didn't do that in the video either.
The question is whether the extra time on dots is worth not using MG.