Existing payment networks already are fast, cheap and I'll also throw in secure. (In Europe ATMs and bank-to-bank transfers are free.) They could easily be made simple to use given the requisite will.
But the Libra website highlight potential usage in developing countries. I may be wrong but in my opinion there is a huge market to take over in the countries where one has a Facebook account before having a bank account.
I can't find the link but I came across an article explaining that in Myanmar Facebook and "internet" are basically synonyms. That's because when most of the population began to have access to the internet it was only via Facebook services that are provided freely thanks to a commercial agreement between mobile providers and Facebook.
Now just imagine if Libra could pull something like that for payment services in all developing countries.