We havn’t made a decision on how to select what’s in each hand yet, or whether they’ll be totally independent or paired together as far as inventory interaction goes; but you will use the hands independently (it’s only restricted so that ‘both’ cannot be used at the same time).
We’ve actually supported dual-wielding in the interaction system for a while now, around the time that interacting with doors etc was changed to be a seperate button rather than a click.
Left-click/trigger = use left hand
Right-click/trigger = use right hand
Each item has a ‘single’ function (except a two-handed item which may have two functions one mapped to left and right hand/click/trigger), Eg: the function of a ‘block’ is to be placed into the world, the function of a ‘pickaxe’ is to do a melee attack of a certain damage type to whatever is in-front of it, whether it be an entity or a block.
The way this currently works, is that a ‘block’ is set-up to be a two-handed item instead, whose ‘left-action’ function is to do a ‘empty hand’ melee attack which I believe does no damage to creatures as it stands but does deal damage to blocks.
This is also one of the reasons (beyond making not super OP anymore) the grapplling hook/hookshot was changed to be a signle action of fire/release rather than a dual-action item, so that in the dual weiliding system we can keep have a consistent interface where you would have the grappling hook in one hand, whilst using a second item in the other hand rather than having to switch your selecttion away from the grappling hook.
So once dual wielding is fully incoperated, the block and other items will be dropped to a single-hand item so that the current behaviour would be to have nothing in your left hand, and a block in your right hand, but you could equally swap that round and have nothing in your right hand, and a block in your left hand instead, or a block in your left hand and another block in your right hand etc.