Avi K
I am not sure what your point is,
Yes Ponovich has Chassidish bochrim who wish to learn in a Litvish Yeshiva to get the Litvishe “derech halimu”, Ponovich also has Sefardi talmidim who come for the same reason.
Most yeshivos in E”Y have that, however they all have a cap on how many they will take since they wish for it to remain a “Litvishe” Yeshivah and the same vice versa.
As fro R’ Shach being oppose, that’s actually not entirely accurate, Rav Shach was opposed as long as there was not any “top Sefardi” Yeshivos, he was actually very for Sefardim establishing “top sefardi yeshivos so the Sephardi Mesorah would not be lost.
There are many letters in Michtavim U”mamorim about this you can look there.