As the title says, I think the “50% increased void damage per Fire Aura” from Dark Shroud of Cinders unique Body Armour should work with Ring of Shields when specced with Immolation.
With a 8 shield RoS setup you would get 400% increased damage to all void damage as long as you can upkeep the mana and shields, which would be balanced since they have their own HP and at high level content they take lots of damage. This, I think, would open up some more unique play styles for the Sentinal, Forge Guard in particular.
One skill I can think of is Shield Throw with the Blackfire Large Idol (converts 100% damage to void). Shield throw really doesn’t see much use in end-game, especially the void version since the Void Knight tree itself doesn’t help throwing skills all that much and Shield Throw’s own tree lacks percent based scaling. Obviously this is just one skill that could be helped, since the buff from Dark Shroud is to Void Damage on a whole it can work with all void skills/spells, though melee would see the most benefit.
I also think allowing this interaction will give Forge Guard a few more options since ATM it’s only really good for a minion build whereas both Paladin and Void Knight have a few viable builds they can play.