> once Instacart has their own (automated) warehouses and can cut out the middleman supermarket

So now they're running a delivery-only grocery chain that has to compete with the well-established brand and distribution network that is popular among their not very price-sensitive customer base.

>Add in self-driving cars, and they're set

Don't hold your breath for door to door that also somehow has to drop off bulky and potentially fragile packages.