BTW, if you know how to upgrade firmware via PC then it is possible...
Technically today, you can download the firmware for a country that supports Samsung Pay and
flash it through Odin.
I wouldn't expect anyone in this thread to know this, but this has been an option for months. If there is any hassle, it's probably the fact that OP's in XDA threads can't fucking organize information and that sometimes it's hard finding a website that has all the latest Samsung firmware that doesn't cap at some obscure slow speed.
I'm pretty sure that I read that India is getting Samsung Pay support, so this may indicate other countries may start seeing this rollout. Regarding Wi Fi calling, I think there was a country firmware that supported that too, but I don't care about that because I get full service everywhere with T-Mobile.
The reason I haven't bothered with changing my firmware for Samsung Pay is that Android has Chase support and it's just as easy to use (Samsung is obviously superior though).
The only thing I'm unsure about is the warranty, BUT I have faced an actual issue before with a phone I've bought internationally.
My Xperia Z3 Compact magnetic charging port detached. This was an obvious defect. I read online about some people actually having issues on getting this fixed for free. I reached out to Xperia US support and they said that I would need to send it the UK since I bought it from there. But, they ended up fixing it in the US at their Texas center and I got the phone back only 5 business days after mailing it in for repair.
EDIT: well after doing some research, maybe there legitimately ANY warranty for the Int'l version (as in you can send it overseas for repair?). Well, there's always square trade...
Anyways, I've been using the Exynos version for many months now and it's been flawless. I can understand though why people wouldn't want to go that route.