Actually, I don't have a problem (on my shadow tank) holding Kephess during this phase. He does hit very rapidly, which is usually a problem, but he actually doesn't hit fast enough to chew through Kinetic Ward. Since KW remains up, shadow survivability is just as good against Kephess as any other tank would be. With that said, it should *always* be a shadow taking the DoT if you have one. Not just for Resilience. Our internal/elemental resistance is substantially higher than the other two tanks, so the DoT hits for much less.
Correct, I phrased myself wrong, of course, a shadow/assassin can keep Kephess and tank him without him dying instantly. But what I mean is that it is more beneficial to have another tanking class (Jugg or PT) as their armor reduces the damage they take since the majority of his bigger attacks during this phase cannot be migrated (which is shadows strong point).
My group runs two shadow tanks, so we just trade off on the DoT and eat it with Resilience every time. Resilience is also super-nice for the leap, since you can just hang out right by the circle and pop it just as he's about to land (you can see his shadow right before he comes down). This also means that you will take zero damage from his melee ability which applies the DoT in the first place (otherwise a 15k hit) and you will be in ideal position to taunt quickly and prevent someone else from being pulled.
Correct, I normally don't place myself up so close to him, and taunting quickly isn't really a problem for assassins regardless of distance since we have a almost instant (unlike PTs), but yes, using your Resilience/Force Shroud at the correct times really lowers the DMG you take.