Yeah, Fel Flame is a very small dps increase for Demonology when using Fel Flame in place of Shadow Bolt. Blizzard needs to address this, hopefully with something other than a Fel Flame nerf.
---------- Post added 2013-06-21 at 09:56 AM ----------
It is modified by Mastery, but its also modified by Demonology's Mastery. What really need to happen is a 10% buff to Incinerate to compensate for RoF nerf, and a small 3 or 4% buff to Shadow Bolt to keep Fel Flame from replacing it. They'd likely nerf us somewhere else, but with the number of nerfs we've already seen this week, I'd hope they wouldn't.
Small note on a bug: MF is still extending the graphical range of Hellfire and Immo Aura, but not the effects themselves.
Edit: After further testing, it appears MF isn't working for Immo Aura or Hellfire when the effect is active on the PTR. Tested and confirmed that its still working for SoC.