Considering the whole reason whatsapp pay got delayed in launching due to data storing requirements (all data to be stored strictly in India). I think we are ok on that front for now
I have enrolled in the beta program for WhatsApp via Google Play so I had the payment option In the new implementation since a very long time (can see a payment from July 2018). In their new implementation they have exposed the UPI ID so compatibility with other UPI apps is ensured. For transactions with other WhatsApp users you need not bother with UPI ID. This dual approach is the same as that of Google Pay.