What would happen if 2 people play in different countries on the same account?

Nah my brother logs into my account to catch region exclusive mons when he was in Korea and Germany and I never been banned for it.

I think the trick is just to NOT do it at the same time and have a 2-hour cooldown difference between logins (could be more but I think that's the minimum for spoofers so it should be the same for multi-devicing across the globe)

Well, last summer, on vacation, I caught mon in Philly, Heathrow, and Zagreb over several hours (2 flights), and on the way home got Dubrovnik, Frankfort, and Philly over a day, with no problems. Can't speak for a tighter window, though, and I really went to those places with my same phone.