With the upcoming update to make jokers instanced, I suggest that they should still be shareable. Up to this point, I've played co-op and joker drops have been quickly determined and shared without issue. The update kinda ruins that aspect of the game.
Ping them to make them visible for other players, something like that.
Look at games like Roboquest, they have a similar instanced-loot system in concept. It helps the flow and co-operation a ton to be able to share.