I think the Soul Swap makes sense, but only if you have Class Trinket and T18 4PC with decent enough hast 35-40%+). You will generate those 2+ shards back before you have to cast SH:Haunt again because your Drain Soul will give you basically a 30+ second Haunt debuff anyways. Also, with Nightfall giving so many 2 Shard procs I often myself overcapped on shards within seconds of opening with SB:SS an SB:H.
But only for single target.