Removing shadowfiend does way more harm than good.
Shadowfiend was an amazing mechanic when it first was introduced. You can time it attack your enemy if lets say you get blinded or stunned/sapped/polymorphed etc. to keep the enemy in combat and maybe cause spell pushback.
You could also at times use it to bounce prayer of healing back and forth in a solo situation or sometimes used void shift (pending if it was bugged/allowed) on it to heal yourself.
It also added a great feature in Cata as a burst cooldown that synergized with shadow orb mastery in that each time it attacked, it granted 3 shadow orbs which enhanced your mind blast and mind spike damage immensely since shadow orbs were tied to mastery and ended up packing a huge punch if you geared right.
This isn’t even taking into consideration the granting of mana it gives per hit which was really good when as history shows, priests had terrible mana regen abilities. For the longest time we relied on passive mana regen from spirit. It wasn’t until later from Masochism affecting SW:D to grant mana from the feedback effect and taking damage from enemies and disperse granting mana back that we had a consistent way to gain mana back.
Point is, the idea of removing shadowfiend is short sighted when you consider what it has done before and what it can do again if just a little bit of care and thought was shown instead of it being ignored.
Now, does the current iteration of Shadowfiend suck? I agree that it’s lacking. But that just means it’s more of a blank slate for blizz to take it into multiple different directions if they just put forth a little effort.
Personally, shadowfiend should act as a DPS cooldown that would be very helpful for shadow, decent for Disc and okay for Holy.
It should take shadows old shadow weaving talent and passively apply shadow vulnerability to the target hit on each of its attacks. This would then enhance its and your own shadow damage making it valuable for each spec, obviously favoring the specs that do more shadow damage. This could have a debuff stack of 5 at 3% more damage and be magic debuff to also help with dispel protection. Since it’s a 3 min cooldown, I see this as a decent amount of time to work as a DPS burst cooldown.
But that’s my idea. It can be something different.
The DPS burst cooldown aspect could exist solely for shadow as a choice node with mind bender as well where you choose higher burst damage for a longer cooldown or higher insanity generation on a lower cooldown.
Again, I rather have more development on shadowfiend interaction than to just out right gut it.