We already have the Auto-Play and Auto-Skill options to facilitate long-term grinding, and the addition of the Lock/Unlock and post-stage Sell All features (as well as boosting the item limits to 60) have helped with the weapon grind. However, a feature that feels a natural fit to a game of this genre, perhaps even right next to the rumble setting with an identical menu set-up, is the option to automatically have items below a certain tier sold: Auto-Sell.
Early game, as well as after transitioning upward through stages, this could be a poor choice as it would impede the flow of items sufficiently good to proceed further and access better gear. Heck, I was wearing a Rare Tier 15 for over a week, not often you find Strength, Crit Rate, and Crit Damage on a ring.
End game though, when you're running through Inferno stages hundreds of time in the hopes of an Inferno item, Auto-Sell would help streamline the game and, much more importantly, help avoid the risk of absentmindedly having a great item drop when your at your limit and seeing the dreaded "Acquisition Failed" rather than your new best gear.