DoorDash is buying Instacart for \$17B — one delivery app to rule them all?

DoorDash just announced it's acquiring Instacart, and even moved its earnings date up for it. They pitch it as 'helping local stores win', but for shoppers this means the two biggest grocery delivery players becoming one company. Do you expect fees to go down from scale, or up from less competition? And will regulators even let this through?