I wasn't overly impressed by the new Manajuma's Set bonus so I had my own idea. The concept is that the Fetish Shaman would become like a Voodoo Puppet and would cause nearby enemies to take amplified damage. It could tether to a few enemies or do split damage in an AoE.
(2) Set Bonus
Causes the your Hex to summon a voodoo puppet that will redirect amplified damage to Hexed enemies.
It only has 1 power and that's to make the summon from the spell 'Hex' take amplified damage and redirect it to the enemies like a voodoo puppet. The other points are just some clarifications.
I get your point that there could be an item to make the set that they have in the data-mined patch notes more useful but this still has good synergy with the new spirit of Arachyr set as well as being good on it's own.
This kind of set bonus would allow single target spells like Haunt and Spirit Barrage to deal large amounts of AoE damage (something preventing them from being used currently)