Driver needs to wait for the second meal to be prepared, pack it together, take a detour to the other place and spend time delivering it.
So your meal arrives late, cold, and crushed after you paid full-price for the delivery.
That's the rub right there.
If you're the winner in the market, can send info to a restaurant to keep your food hot (or even hotter than normal) and can schedule it perfectly it will work.
Once you spend a couple of billions into the infrastructure to make it happen, you can totally make a couple of hundred thousands worth of profit - 2020 Startups.
I'm not sure what exactly you think restaurants can do with that request. A small subset of places will have a heat lamp, but that still doesn't really preserve quality, just heat.
Restaurants would soon figure out how to use a couple of timers to get every order done on time.
There could also be a deeper integration to ensure that, for example, there are no more than 3 orders worth of fries being cooked at once, or no more than 2 pickups per minute scheduled, to avoid overloading that part of the kitchen.
And if it turns out customers are willing to pay restaurant prices for McDonalds quality delivery, then McDonalds themselves will start a delivery service to compete with you.
The quality of the food delivered is dubious, to put it mildly, just by the very description of the process.
My driver picked up my meal (from about 10 blocks away), then proceeded to drive downtown to pick up another meal, then to the other side of town to deliver it, then finally back to me.
My food arrived almost 2 hours after I ordered it, cold, soggy, and leaking in the bag.
It's not illegal, just difficult (don't ask how I know)
Sprig only offered 2-3 dishes.
If we knew what we wanted ahead of time, scheduling delivery ahead of time would make it easy... since you could use a delivery route (to deliver 2-3 items nearby).
A single winner may be able to make it work since you can do 1-2 pickups and deliver to two nearby homes.