nice, interesting indeed. though the guy screwed up his maths a bit (and it's on the american forums so my damn account details don't work there ....argh lol)... the multipliers don't add together, they multiply together, it's not a 24% from soul-siphon+20% SE, 20% haunt, 10% SM. it's 1.24*1.2*1.2*1.1 = 1.94 = 94% multiplier so the damage will actually be higher than he predicted.
the whole idea though is amazing. it gives us a larger incentive to drain soul the end of a mob, so decreasing the chance we'll run out of shards while also being very mana effecient and supposedly, really good damage :)