I think this is a pretty smart play. I (and a lot of Brits, I'd guess) use WhatsApp about every 7 minutes. Sure I could send money through PayPal, or bank transfer or any of the other apps I have on my phone that facilitate it - but WhatsApp would make those payments to friends just that little bit more convenient. Why open PayPal? Why make my mate open PayPal? I'll just send it next time I check all my chat groups...
This is probably also a pretty smooth intro to Libra. Start with "we'll send X pounds via Libra instant transfer: £X = XL", end with "You have XL in your account. Withdraw to £".
In Canada, bank transfers are so seamless that I see no chance of this ever gaining traction. It's called Interac e-Transfer, and all domestic banks are part of it. All you need is access to online banking, so it's universally available. It's free, too (for personal accounts).
The way it works is the sender signs into their online banking and initiates an e-transfer. The sender doesn't need the recipient's banking details, only a phone number or email address. The recipient follows the link in the email/SMS message they received, signs into their online banking, and selects the account to deposit the funds into. The entire process is immediate.
If the recipient has registered that email address or phone number to auto-deposit into a specific account, all the sender has to do is type in the amount and hit Send. Otherwise, they will have to create a short question with a secret one-word answer that the recipient needs to answer correctly.
How could WhatsApp payments be better than that? Not everyone has WhatsApp, and if you want to use it you'll need to go through the hassle of linking your bank account.
The hassle of linking your bank account is more of a hassle in countries where that isn't necessarily easy to do. (For example to link an internet banking account to your traditional bank in Canada, you usually need to send a personal check in snail mail.)
In China, where mobile payments are ubiquitous, the process of linking your bank account is just typing in your name and account number, and entering the one time pass code your bank just sent over SMS. Now you can pay for everything - not just individuals on your contact list, but literally anyone who also has the app installed - just by scanning QR code and entering your PIN. The recipient doesn't need to sign in or confirm anything, it's just done.
Don't underestimate the convenience of this setup. I do like that Interac eTransfer doesn't force people to install a proprietary app to transfer money, but can you really see it replacing cash in a grocery store or helping people split the bill at a bar?
I've tried to split the bill this way too when I lived in Canada and didn't find it quick and easy at all.
First everyone needs to log in to internet banking, then they need to find out the email address of whoever is picking up the tab, then they need to wait for that person to receive their email notifications, then that person needs to log into their online banking to accept each transaction one by one... With Alipay or WeChat it is much more seamless, and the whole process can be completed in literally a few seconds.
It might not seem like much of a difference (a few minutes vs a few seconds), but once people get used to that convenience, I can't see them wanting to go back.
This is probably also a pretty smooth intro to Libra. Start with "we'll send X pounds via Libra instant transfer: £X = XL", end with "You have XL in your account. Withdraw to £".