I've had an interlock from DUI. Mouthwash, yes, but it's pretty simple to not blow a false positive. Have a drink of water or literally anything non-alcoholic before getting in the car and the mouthwash alcohol will be gone. I think the bread, gum, energy drinks, and everything else setting off an interlock is largely nonsense and an excuse people use when they get caught not wating long enough after drinking to try to start their car. I never changed my eating or gum chewing habits and not once ever had a false positive. I'm not saying it can't happen, just that it's extremely unlikely and can, again, be solved by taking a drink of anything and getting the bread, gum, or whatever sugars out of your mouth.
The fact that interlocks might once in the bluest of moons give a false positive and stop you from starting a car for a few seconds while you rinse your mouth out isn't really a good reason to not have interlocks in cars, IMO. I think a bigger issue is you might have to make an exception for someone who has COPD or possibly a respiratory issue that affects them from properly being able to blow in it. It's not just a quick little blow. You have to blow pretty hard and consistently into an interlock emptying out most of the air in your lungs.