I’ve always found fun to gamble in D2, Torchlight, etc. Can’t say anything about D3 because I ditched that game in 2013.
I’ve searched the forums and turns out no one has ever mentioned gambling here… It’s either unappealing or people just forgot about it.
You guys could introduce a new quest (a hard one), to save x npc. And implement a new currency (a hard to find one), to use in gambling. Rewards for gambling could be items and more stuff, up to you.