Spirit Sword has crazy damage, and you have another skill which gives you avoidance, but not tankiness. You are still squishy. They are not warriors, they are rogues!
Unless we can take mitigation through crafting, I dont think a tank KE will be possible in higher difficulties. The frost 50% passive is huge, but it is the only mitigation we have seen for KE so far...
Maybe we can start being mages, then unlock specialization and become rogues, and lategame when we have the correct talents and crafted gear we can become tanks... Talk about variety! 
Oh yeah? I'm tanking everything since level 1! #AssQuisitor (or something
)
Now, i do hope that heavy armor(real heavy armor, not just light armor that looks heavy, because we know they are available), are available until around mid game, i woulnd't want to spend a big part of the game grasping for mitigation.
In all honesty, there is no point to give someone power for just a few last battles. The biggest part of the game will be gone. If you can't customize yourself freely from a relatively early to mid point in the game, then the talk about customization was for show.
I don't know exactly how it works obviously. It could still be available early, or some can be available early. I guess not everything is available at the same time.
But it's a reminder to the devs, that aesthetics are important, and people want to look cool, as they envisioned their characters. With all the hype about customization, i honestly hope the hype, when you told us we would be able able to wear plate armor for Mages(and not at late game,never heard anything about that), was not just for show.
But seriously Kage, i don't see the squishiness you're talking about. With correct rotation of abilities that were not even optimal for tanking, and with light armor, the KE was receiving almost no damage on hard. When Mike neglected his cooldowns to show the other characters as well, that's when the defenses went down and received some damage. And he didn't even use fade cloak.
Anyway, to each his own, but yeah, KE can fill a lot of roles as i see it. Melee range damage, utility and support, tanking, whatever.