I guarantee you that this will not have the perceived level of anonymity that Bitcoin and other cryptos share. The publicly visible ledger may not reveal who you are, but Facebook and its partners will know.
Related to that above, maybe then also cross-border payments. For example migrant workers sending money back home.
Quick Googling shows a report from 2017 which says in summary "About 1.7 billion adults remain unbanked—without an account at a financial institution or through a mobile money provider. " https://globalfindex.worldbank.org/
I'm Whatsapp-ing my son who is a student, and he tells me he needs money. A button pops up onto the screen saying "Give Michael $50".
I click the button and the transaction is done.
With our marketing hats on we like to talk about what we can do with "one click".
I've personally never seen a one click system in my life - this could actually be one, and for one of the most fundamental and valuable human activities - paying someone.
You don't need a cryptocurrency for that...
Quick Edit - I think Apple Pay can function this way via FB messenger?
Why? Are there limits on accessing your own bank accounts IRL?
> Would bots spam everyone on earth requesting $50?
No. Facebook would not allow that to happen. They control their user base with a tight fist when it affects their own revenue (user privacy less so).
> Do you have to maintain a list of who can and cannot request money from you? It just seems like there would be a lot of headaches with that system.
Why bother? Yes it could be uncool behaviour to request money from people, especially if the request had some social pressure around it.
But people can (and do) already behave in uncool ways on Facebook and the world goes on.
The potential revenue from being a money pipe would motivate Facebook to effectively deal with all of these problems.
The point for Visa et al. is to A) hedge their bets against possible long-term disruption from crypto in a safe, centralized manner, and B) to attack crypto head-on by satiating the curiosity of those who may want to dip their toes into the water, creating a walled garden that no one bothers to peek over.
The point for the user is to... umm...
So purely virtual payment methods will be hard to use.