As Patch 3.3 nears, more and more information is released from Blizzard. Today there were a bunch of changes made to the 3.3 patch notes. Some of them showed how some of the Shadow Priest abilities will change in the future.

Priest Shadow Talent Changes
o Improved Devouring Plague: This spell now deals 10/20/30% of its total periodic effect instantly, up from 5/10/15%.
o Mind Flay: The range of this ability has been increased to 30 yards, up from 20.
o Shadowform: This talent also now causes Devouring Plague, Shadow Word: Pain, and Vampiric Touch to benefit from haste. Both the period length and the duration of these spells will be reduced by haste. In addition, the mana cost has been reduced from 32% to 13% of base mana.
o Vampiric Embrace: This ability is now provides a 30-minute buff that cannot be dispelled, instead of a target debuff.

You can find all the 3.3 PTR patch notes here.