It is a interesting thought. My first thought was a Walbro carb with a servo built into it for controlling the throttle. It isn't a bad thought to have.
But whatever one does it has to be relatively inexpensive though.

Even with fuel injection, you still have the throttle to control on the throttle body. So we still need some sort of a servo like mechanism to control it.

One other thought is to use a solenoid like arrangement for controlling the throttle. This has been used a lot on various things where you have a plunger that moves in and out that is controlled by varying the voltage level applied to it.