Probably backing up physical "version" of currency with BLOCKCHAIN will be better than with metals

I don't think so.
I think virtual backed by physical will be good.
we will not say a 1 usd physical coin worth 100 or 1,000 usd,
so it don't need backed by virtual blockchain.
I thought you might not know, we will distribute the coins close to the cost price,
so you don't need to worry about they will not worth money.
even the recycling plant will accept them with good price because it is the money.
so if you can make physical coins, we will very happy about that because you can help us.