My understanding is that the plan has always been that the groups will eventually be "merged," that is, on the basis of English language services. This was to be a temporary arrangement based on transition, not a separation.
Perhaps more needs to be done proactively to facilitate the merge, not sure of the status.
Why English and not Korean? In other words, this "transition" In my most humble opinion need not be based on a language but on a confession. Of course this is just an opinion from the popcorn seats.
The idea was, I think, first generation immigrants who still had not mastered English, their new national language, would only temporarily be holding services in Korean. They would not be demanding translation of everything in the denomination they chose to be changed for them.
Like Italians, Poles, Checks, and others before them. They would intend to assimilate, not "balkinize," and thus be in the mainstream of their church, as it were.
Now, were Americans in Korea, one might expect the same thing....