Did you read my post? This would be akin to declaring war on PPP. It's like trying to gouge London from England, Rome from Italy. simply not going to happen. Not this century. Note what I said.
Karachi was and is capital of Sindh going back to British Raj. Any attempt to change boundary of Sindh would be giving Sindhudesh movement a steriod injection like the imposition of Urdu on Banglas was in 1950s which festered until it exploded in 1971.
Sindh is Sindhi majority. Any such move would be seen as gerrymandering and cause strife in Sindh. Keep in mind Sindhi's are majority. There is ocean of them around the urban areas.
It would also be constitutionally almost impossible because Sindh would not give assent to such a move.