The summary of what is known right now: If it goes live as it is now, it'll be our weakest dps talent. In fact, if I had Shadowy Apparitions right now in live, it'd be contributing a grand TOTAL of 14.4dps, or 4.8dps per point. As a point of reference, right now on my character Improved Spirit Tap (our current weakest dps talent) grants me a bit over 30 spellpower, which is over 60dps on Mind Flay alone. So IST is at least 30dps per point for me now, while SA is 1/6th of that. And IST is a talent you only sink points into if you have the 4p t10 bonus and have the free points.
And if I were to be a complete noob and cast SW:P on multiple targets while running around like a twat, SA would give me 144dps per target. With 10 targets, I'd get 1440dps worth of SA procs, at the expense of running around like a git. But if I say, stand still for 2 seconds, I can get over 4800 dps with a single Mind Flay, and when doing this, my dps for SA drops back down to 14.4dps per target.