From the 0.8.5 patch notes:
The Soul Gambler within the Soulfire Bastion dungeon took much of the Gambler’s role, where you can exchange soul embers taken from fallen enemies for loot after killing the dungeon boss.
Whereas The Vaults of Uncertain Fate within the Lightless Arbor dungeon was added as a gold sink allowing players to spend their excess gold in exchange for (potentially) hoards of loot after killing the dungeon boss.
Also, you can spend your gold on additional stash tabs with each tab increasing in price and a maximum of 200 stash tabs to purchase. The dev’s have talked about providing additional gold sinks in the future, though we just don’t know what those will be yet.