The argument was made that fuel lines between E10 rated and flex fuel vehicles are different. I contend they are not. Simplicity in the logistics and supply channels is paramount in auto production to reduce overall costs and parts mix ups. I have hauled hundreds of loads of production parts to assembly plants. The same lines and such are going into flex fuel vehicles and E10 vehicles. Complications are avoided, like having E85 rated components in a E10 rated vehicle, or E10 rated components in a flex fuel rated vehicle. If a auto maker is producing both E10 and flex fuel vehicles, they use the same flex fuel capable components. The only real difference is an ethanol level sensor and ECM programming.
But more likely, even E15 would not be actually E15. The regulations say a maximum of E15. It can contain any level up to that. E10, the same way. Even E85 has a level between E70 and E85. Again, a maximum of 85% but can have less. There are many instances where E10 doesn't have even 8% ethanol. It is not inconceivable that much of what is sold as E15 will have lower than 15% levels, probably 11-12%. And it is quite a stretch to think that 1-2% higher ethanol in fuel is going to grenade a fuel system that have already been approved and using E10.
Seems this whole argument over E15 is a wasted effort and supported by irrational paranoia. No one is forced to use E15. Even any mandate by EPA for it to be available, E10 will still be at the same retail outlet. E10 is not going to be eliminated. This is more retailer focused to get higher blends at the pumps. That is why there has been a push for some time get retailers to offer blender pumps that will allow E10, E15, E20, E30, E50, and E85 all at the same pump.
Frankly, I haven't seen such a level of paranoia over something since the old Cold War days when we might be obliterated in a massive nuclear exchange. Some folks need to take a chill pill.