Witches and Shadows need to take Chaos Inoculation if they're going spell-heavy. I see three reasons for this:
1. The high amount of chaos damage in Act 2:
Viper Strike on spiders and squids
"Damage over time aura" on bears in waterfall cave
Vaal Sharpshooters (they can lance you in packs from huge distances in some rooms, and are very mobile)
"Deals Chaos Damage" modifier for Thralls and some other human enemies
Poison Arrow on skeleton archers and some human archers
2. The low amount of +life nodes for witch and shadows compared to the plethora of +energy shield nodes; the low amount of +evasion nodes for the shadow; it is much easier to find gear with +energy shield than +life
3. The increased cost of traversing the tree (compared to the old tree) has made travelling to Marauder or Ranger space to grab +evasion or +life difficult.
I don't know GGG's mission statement when it comes to class identity and survivability, but I think all 6 classes should be able to acquire some healthy degree of defense should they choose to. The Marauder is no more a tank than a witch, in theory. In practice, a Marauder should perhaps more defensive options available to him, but a Witch should not be synonymous with "squishy glass cannon", not with such a large passive tree in this game.
1. Move Blood Magic a little bit closer toward the middle. I think one of the stronger reasons for a Witch/Shadow to take life is so it can be used to cast spells.
2. Add 1-2 evasion clusters to the Witch and Shadow.
3. Add 1-2 life clusters to the Witch and Shdaow. One node should add +30 flat life.
4. Remove Chaos Inoculation and concentrate chaos damage in Act 2. I love chaos damage as it adds challenge and difficulty - but if I cannot resist chaos damage at all, it should be concentrated into one zone, like the waterfall cave, rather than spread out over act 2, requiring me to build in a certain way with every character. Chaos damage as a whole punishes players who don't stack life or energy shield.
5. Add a new energy-shield releated keystone.
6. Increase the breadth of survivability options for the shadow and witch. It's okay to have a few +armor clusters I think, off the beat and path. Either that, or you need to retool the entire middle section and make it more accessible - and put a wide array of interesting defensive clusters there.
7. Consider some flat +life regenerated per second nodes for the witch. It would certainly be interesting for Witches to have high energy shield, low life pools, but have good life regeneration to combat chaos damage.
8. Consider "tuning up" this area of the tree:
It could use some love. If you're going to use pain attunement, it's going to require a lot of thought. How about putting a few +life regen or +max life nodes here? Or perhaps a good evasion cluster? Having low life with a lot of evasion would be a great strategy. A small armor cluster might be a good idea too.
Oh and one small note, getting that "bloodthirst" node is really kind of expensive. You can get the same amount of +crit chance for one less point by taking that cluster of +crit left of it. I guess you could get both crit clusters but... erm it just seems a bit silly is all. Like there's too much critical chance in the area when there could be some defense clusters the Shadow desperately needs.
edit: *sigh* Another dead hardcore shadow :/, was level 24 with 200 ES and 200 life, one server hiccup and I'm toast, even when I'm building as bulky as I can