Yeah, this is how most E85 engines generally work. They have a E15 engine map, and an E85 and map. And use sensors to figure out which fuel is in the tank and which map to use.
Stock cars generally don't take full advantage of the octane benefits of E85 because they will blow up if someone fills the tank with E15. But in the aftermarket world, "corn powered" cars make substantially more power, especially turbocharged ones. They have the benefit of owners that understand to manually switch maps when changing fuels.
Agreed, there are several aftermarket ethanol content analyzer sensors available, easily installable onto the fuel line of any car. These supply an ethanol % reading to the ECU and allow for aftermarket tunes to adjust timings based on the current fuel blend. No manual swapping necessary.
Stock cars generally don't take full advantage of the octane benefits of E85 because they will blow up if someone fills the tank with E15. But in the aftermarket world, "corn powered" cars make substantially more power, especially turbocharged ones. They have the benefit of owners that understand to manually switch maps when changing fuels.