It means that if this study were accepted, all coins will be a nickel composition on their exterior; like US pennies today are copper on the outside. Nickel clad zinc will be what nickels, dimes, quarters, halves, dollars (and/or whatever coins the future holds) are composed of.
Think nickel response on your machine. That's what I'm saying. Of course there will be variation by denomination/size/mass but it'll all be down in the nickel range- or more likely a new range of its own since the core would be zinc if they go that route.