The french are already concerned per their finance minister.
But FB Libra could be the turning point in the death of fiat currencies.
Sure you have to register like you would have to with a bank, sure FB has never been known to be secure in anything it does, and the whole FB libra coin is not a BTC, in function or concept. It is a centralised coin, but that adds the ability to refund if any hacks were done.
Of course FB can unsubscribe you at anytime & probably may your coins along with your FB page inaccessible if they wanted to.
But what FB really does is intro another 1-2 b users to the concept of payments without fiat.
or perhaps the banking cartel are planning that FB Libra will be a new global currency.
https://www.coindesk.com/libra-white-paper-shows-how-facebook-borrowed-from-bitcoin-and-ethereum