I think Bitcoin has the potential to overwhelm paypal but there are two things I'm not sure about Bitcoin that are unstable prices and too long transaction time.
Too long transaction times are already a non-issue when accepting zero-confirmation payments.
Zero confirmation payment is impossible to implement. Because when you use blockchain you can just use double spend. So the confirmation is unlikely to come then the amount of bitcoin back to the sender wallet. Using zero payment system is at risk to apply