I just see a huge headache with paypal even if they accept bitcoin, with their chargeback and refund policies. I try to avoid using paypal whenever I can.
Here's what I think PayPal could do:
PayPal user "sends"
BTC to PayPal by having PayPal sweep their private key (note: sole private key possession is proof of ownership). PayPal converts
BTC to their local fiat currency. Within the same login session that the
BTC was sweeped in, PayPal user can send the fiat to another PayPal user, or initiate withdrawal to their own bank account. Yubikey or other industry standard 2FA would be required to do anything with the fiat after the login session is terminated.
Fiat payment is now irreversible because you can't claim your 1) credit card 2) bank account 3) PayPal account 4)
BTC exchange account (none of which provide private keys to users) was stolen. For fungibility, PayPal is held harmless for users/exchanges not properly securing their private keys, just as they would be held harmless for someone placing their wallet full of fiat on a bus bench and walking away, then a thief not obeying found property laws, taking the money in the wallet, and buying a PayPal money loading card with it.