If you could tell Nexon one thing...

It means that everything ever released after the point they fork and diverge will also have to be rewritten before it can be added.

No matter what kinds of delusions you're under, what you're asking for is not reasonable. What you've said is commonplace, isn't. Patches to an app while it's live, yes. A completely new redo of the same app while the original continues to also simultaneously develop, no. That idiocy is rare to non-existent because it means you're trying to develop a copy of something that's not staying in the same shape while you try to copy it. On the occasions it happens it means the team working the "new" project has to continually revise their own requirements to account for new stuff so it gets implemented in both, or as happens more often, the changes get lost entirely and have to be added back in later after the original version is dead and gone and the new one is the only one still standing, but in your scenario that's not even possible because they'd have to keep both versions alive for all the locales still using the old version because there's absolutely no way every locale could switch servers and/or clients simultaneously with only one team supporting them.

You don't have sufficient experience programming a production app on a team scale for multiple locations to argue this subject competently, so I'm considering this sidebar dead and done.

Actually I do have experience programming a production app (developed about 8 so far in my career, 3 of which were replacement apps), (multiple locations lol, is just a minor inconvenience).

You don't understand that while the replacement is being developed, the old system's updates would be minimized, to heavily reduce such issues. The team working on the current system will be part of the design process of the new system as well. This "idiocy" happens all the time. It's called reality. When an an old system is out-of-date, a new system replaces it, and it usually gets developed while the old system is still live so as not to interfere with business.

And as for locales, the switching process for each would be gradual. Not all at once.