In resume :
Replace the +skill class on end game items with +1 All skills
Why :
This WE, I tried to find what end game stuff can fit my current character and it’s really hard to find stuff optimized for him.
One of the main problem is the lack of +all skill on 75 legendary or epic gear.
All this items add +1 to one class, and if you don’t play this class, you loose a lot of power (and lot of skill points)
My example : A Trickster (shaman+nightblade)
I use 2 handed weapon, dealing physical and frost damage mostly.
Nightblade : for amarasta’s blade burst, Ring of steel (frost), Veil of shadow (night chill) and some utilities
Shaman : for 2H damage and life regeneration, with savagery.
https://grimcalc.com/build/4zYCOVR
If I look what stuff exists, +shaman give mainly bleeding damage or pet damages, and +nightblade give bleed or frost, but mainly for 2 Weapons fighting.
The only 2H weap suited for my class is the Bane of the Winter King, which give + shaman and nightblade, but also pet buff.
For Armor the only frost set for nightblade buff 2w and need at least 1Hand weapon to activate the +1 skill, 2W for the whole set bonus.
My build is by far the best 2H build I ever build, so in a way he is fully viable. But I’m not sure I can make my way in late Ultimate because of lacking those + skills 
With + all skill instead, it will allow custom builds to get same advantage of any end game items combination.
I don’t like to play games like someone else decide how to play, so I rarely use obvious combinations 