The rich do not, in general, possess Scrooge McDuck vaults full of "prior government backed currency". The assets of the wealthy are generally real assets and business investments.

Cash is such a poor investment that the word "investment" typically means trying to find something more productive than holding cash. Neither do alternatives to cash have a reliable history of benefitting the poor. In the US there's been lots of attempts at local currencies; they tend to fail naturally without government interference. Recently, cryptographic alternatives to cash have mostly served to benefit crypto barons and scammers.