There are some coins available on PayPal, not only Bitcoin, but there are also ETH, BCH, and LTC. It is still the beginning of how PayPal makes this decision. And it doesn't mean that PayPal will never list XRP. probably, some days, they will also consider XRP.
However, don't say about replacing BTC with XRP because it will not make sense. BTC is however more promising than XRP.