This is just my wild speculation, but reading the melt ban makes me think it was designed to protect zinc cents/CuNi nickels first and foremost. Copper pennies have existed unprotected by a melt ban from 82-06. At 10-20% of the penny population, if all the copper pennies disappeared over 1 year (obviously much faster then it would ever happen because of those penny jars) the Mint could easily replace them. Remember that a large number of pennies drop out of circulation anyway every year.
In Canada the Mint makes plated steel coins without any noise (I've seen yet) about needing to change the alloy or reduce the cost. The US has copied the Canadian Loonie with the Sac and Pres Dollars. Why not move to steel plated as soon as they get congressional approval. After the switchover, no need for a melt ban to protect the 10-20% copper pennies. Nickels could be a continuing problem though since 100% of nickels are potential melt targets.
“The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.” – George Bernard Shaw. Why Copper Bullion ~~~ Interview with Silver Bullion Producer Market Harmony Passive Income blog
I got a plastic penny in a bag I sorted today. Since pennies aren't used in vending machines, what would keep them from making them out of plastic like play money?