Taco Bell has a pretty brilliant business model. Most of the menu items are variants of other things it sells. You can get a taco, a burrito, nachos, a chalupa and who knows what else that all use essentially the same ingredients but package them in a different delivery device.
That means the chain can add one ingredient — a new protein, a new sauce, or perhaps a changed take on queso — and use that to really shake up the menu. It is a model with which the Yum! Brands (YUM) chain to look like it’s constantly evolving and trying new things, when really only making bold bets on rare occasions.