I seriously doubt it will overtake Paypal for many reasons, not the least is the massive regulatory hurdles that must be overcome before it's actually processing live fiat transfers to actual ecommerce sites like Paypal is, which gets to avoid a lot TILA because its just an intermediary. How EFTA that requires consumers to be allowed thirty minutes to cancel an electronic transfer? If REQ becomes mainstream, how exactly will that be implemented in an immutable blockchain? Everyone should read Paypal Wars to see just how many regulatory challenges there are that need to be overcome.

And its not just Paypal, you have Stripe, Square, 2Checkout, all sort of competition.

Assuming it does get past these regulatory challenges, I can see it serving as an ecommerce gateway between other fiat depository organizations and cryptocurrencies. Lets be real, Amazon will always prefer the US Dollar to any cryptocurrency.