PayPal's pay in 4 will still have positive impacts for...

PayPal's pay in 4 will still have positive impacts for merchants, such as increase in basket sizes and conversion rates, that's pretty obvious. I do agree that there is no way Afterpay users would swap to Pay-in-4 except where Afterpay isn't offered (which is a lot of stores, especially in the US) so you might naturally get people using Pay-in-4 just for that reason.

The threat to Afterpay isn't really consumers shifting from Afterpay to Pay-in-4, I think the risk to APT is the slow-down in consumer and merchant acquisitions as new consumers would almost inevitably be introduced to BNPL via Pay-in-4 due to the wide reach of PayPal.

For me the risk isn't enough to sell APT, but it's certainly something I'll be keeping my eye on over the next 48 months.