According to the official forums, it's about a 10-15% dps buff by fixing this bug, AND due to Spiked Collar, it's now MORE OPTIMAL to use a ferocity pet for survival one again.Survival Hunters' Mastery will correctly be activated by pet auto-attacks.
Unfortunately, Mortal Strike can still proc mastery, so we're still stuck with a River Beast, Scorpid, or Carrion Bird, but it's a step in the right direction!
People are currently testing to see if Snake Hunter is worth taking still, or if Murder of Crows will be better, as the new Mastery fix apparently makes it really easy to get to 6 stacks without needing Snake Hunter. It also apparently makes Mastery and Haste more valuable, with the top SV hunters agreeing we want to -try- to get to at least 8-10% mastery.