The gambling feature in Diablo 4 will work similar to the one in Diablo 2[1]: there will be an NPC to exchange gold with for a (slight) chance at a superb item:
"We're trying to be more strict with gold at a personal level for players. The gambler, kind of like in Diablo 2, you can spend gold to gamble, so it's going to be an improvement on Gheed and Kadala, but it takes gold. If you can imagine, if I can gamble for the best items in the game, then gold will be meaningful at all times, so that's our plan with gold and gold sinks."
David Kim · Former Diablo 4 Principal Game Designer ·
Xiphoid has been playing the Diablo series since the original's release in 1997. He created one of the largest Age of Empires fansites in the late-'90s and early-'00s. Now, he runs MythicDrop.com, aiming to make it the premier Diablo 4 resource.