Scrip usage can be seen today with the issuance of closed user tokens by casinos and electronic games for use within their environments only.

Crypto-currencies were developed out of these use cases but were supposed to go one step further towards becoming money (and therefore alternatives to sovereign money).

Crypto-currencies, and even BitCoin, have struggled to establish the last function in the hierarchy of money, the unit of account, as defined by Adam Smith in the Wealth of Nations.

By not valuing goods and services in a particular currency (such as BitCoin) has meant that they have not been priced in that way and therefore have not been accepted as a general medium of exchange.

The concept of legal tender and pieces of legislation (such as the UK Employment Rights Act 1996) have embedded the usage of GBP in the UK as the common medium of exchange.

Crypto-currencies can continue to be used in closed user groups. 

A user group of 2.45bn of Facebook subscribers, however, cannot be considered to be a closed user group.  If successful, Libra could result in a huge amount of sovereign money being taken out of general circulation or, even worse, the Libra Association becoming THE MOST POWERFUL CENTRAL BANK IN THE WORLD!