You don't know my usage patterns or what network I'm on (or plan to be on), but your vote of confidence is noted.
Indeed we will.
You clearly haven't been paying much attention to these forums. Before long, there are complaints about how older model iPhones run slow under the current version of iOS. I prefer my phone to be quick and without any stuttering.
Look, sticking around with the iPhone 5s is a perfectly valid use case. If that's what you want to do, great. Go for it. But clearly that's not for everyone.
Actually, the payment system is not an Apple proprietary technology, but an already recognized NFC standard that exists on a number of credit and debit cards already. My Chase debit card has been working fine this way for years now. If a business already accepts NFC based payments (like PayWave, Amex expressPay, Citi Blink), then this will work there, too.
What HAS changed in Apple's case is the back end, and who's doing that processing. In this case, it's Apple negotiating agreements with a number of large banks, which they've already done.
Then don't do it. Enjoy your 5s, I'll enjoy my 6 Plus.