These three are actually quite different. Apple Pay and Google/Android Pay are only systems to deal with credit and debit cards using smartphones and NFC. PayPal, on the other hand, is - in addition to offer a credit card interface - a kind of "online bank". So it's actually a bit more similar to what Bitcoin offers.
Can Bitcoin replace these credit-card-based systems? It is certainly a challenge. For example, for merchants like hotel owners credit cards have many benefits which Bitcoin can only offer in a very limited way. You can reserve payments without actually making the payment, or offer automatic refunds - that would, if implemented in Bitcoin, need at least, a pretty complicated contract.
NFC-based processors whose only purpose is to not having to carry the debit/credit card with you are more simpler to replace. NFC-based wallet and Point-of-sale systems would, however, be needed (it would actually be easiest if Apple and Google incorporate BTC to their payment processors). And then there is Bitcoin's notorious volatility, which is limiting "direct adoption" by merchants because they have to take the risk of losses when the price goes down.
I think volatility is the biggest obstacle right now, the other ones are solvable with technical innovations, most of them are already possible but lack adoption.
Yes. Volatility is the main issue that Bitcoin is facing, since it emerged on the market. On the other hand, technical innovations will solve various issues related to cost-efficiency, speed, and privacy. One of the big improvements for Bitcoin, is known to be The Lightning Network itself. If successful, then large payment processors like PayPal, Western Union, and MoneyGram could become threatened by Bitcoin. The pioneer cryptocurrency will be able to retain its decentralization and security, while at the same time being instant and dirt cheap. Only then, merchants will prefer to deal with Bitcoin than centralized alternatives.
Despite this, the uncertain price of Bitcoin each day, would make merchants want to exchange it to Fiat quickly. While stablecoins provide a better option than Bitcoin and most cryptocurrencies out there on the market, they're still largely unproven.
Nonetheless, I believe that payment processors will be here to stay for a long time. There's a possibility that they will adapt to Blockchain technology in the future. And if this happens, then the hopes of Bitcoin beating centralized payment processors will become distant like never before. Just my thoughts