You can't prevent ALL allergens from ending up on planes, but nuts are so common.

Another thing airlines could also do is not have all the in flight snack boxes contain nuts. I was looking on an American flight and had I wanted an in flight snack box, I would have been out of luck. My nut issues aren't affected by cross contamination or airborne, but I still can't *consume* nuts without...well, having effects you really don't want on a plane. Ahem.

I'm not allergic to peanuts, just tree nuts. I like peanuts. I don't take them on planes, just in case.