I play Necro Feral in PvP. Not rated tho, just did 1800 rbg as tank to get some gear and have fun with it in bgs and Warmode. Especially on warmode i fight all kinds of classes with often enough pretty darn good gear.
But i can confidently attack anyone at this point. The Burst is just massive with adaptive swarm, tigers fury and trinket, dots are ticking like crazy.
Rake crits for ~4k, rip crits for 3k+, moonfire crits for abt 2k and feral frenzy ticks for up to 7k. Plus melee hits, adaptive swarm damage, brutal slashes etc…
In unrated BGs its obviously even crazier because of berserk. As an example from my last BG my frenzy crit for 11k.
As for “rotation”, i open with rake, brutal slash into > savage roar into -> tigers fury+trinket+adaptive swarm on target into -> feral frenzy -> 5points rip, followed by moonfire.
Rotation of a few seconds and once its done players start melting down and often enough they dont even realize whats happening.
As an example i had so many mages who tried to blink away or cauterize and you watch them just die, paladins who didnt bubble cuz they didnt expect damage or didnt respect.
Especially if dots crit it is amazing and i wouldnt ever want to go back to nightfae. I am using the 40% dmg legendary btw, regret i didnt try it earlier.
I have also seen ferals using the same spec in 2v2 successfully. I am just not the Arena guy so i cannot really say anything about viability but i would be suprised if it would be worse than the usual bite spam build. At least in my experience in World PvP, Bgs, 1v1 and 1v2/3s, spamming bite is nowhere near as deadly and has the pressure that dot build has. Also you dont rely on Berserker in any way.
Thats just my opinion on this. I love it alot and i cant wait for Adaptive Swarm to get the 5% dmg buff on dots.