Kids from the future will be confused

They will say "burn it with fire"!!!

By that time, there will probably be some other popular contraption around

True

Maybe sometimes. And maybe they will question it, but other icons have evolved out of outdated technology and most young people accept this is the icon because that's what it is. I've seen a post where a kids asked "Why would someone 3D print a save icon?" In response to a floppy disk. I don't think most kids will even question it--especially with all the icons that float around that aren't based on anything--or are based on something obscure or outdated