no. just. no. there are two main reasons in my mind why they wouldn't merge them.
1) JP viewership is high af. If you merge them with KR. Then Rito are losing a ton of money
2) KR hates JP. So uhh. A lot of pros will be very mad. And they 99% likely won't like it.
3(minor reason)) JP orgs are investing heavily into this game and they most likely will invest much much less if the challengers and regions are combined.