CalGreenCard
Registered Users (C)
It is not tax loopholes, these are tax laws.
The loophole comes in when it is sometimes possible to, legally, avoid taxation in either country by filing as a non-resident in the USA during the year of departure.
In this case it would depend, in part, on the laws in Korea and, perhaps, any third country of residence--and that is beyond the scope of my interest in this thread. The OP's wife needs to research whether there is actually a substantive advantage in her case.
Indeed this whole thread is in the wrong forum because potential US citizenship is not in play here--the issue is whether the spouse from Korea remains an H-1B or becomes a GC holder. This thread belongs in the "Family Based GC" forum.