Pakistan needs to be balkanized and de-nuked.
Maybe in 20 years, the independent countries of former Pakistan (plus maybe Bangladesh and a few other neighbors) can enter into an economic union with India.
Maybe 20 years after that, it becomes EU-style union.
Maybe 20 years after that, it's a reunified India.
That is the ideal situation, to me.
It's all very well to sit in the west and comfortably opine on where the borders should and shouldn't based on a cursory understanding of different ethnicities in Pakistan (or elsewhere) but at the end of the day partition is a lazy and fraudulent solution for geopolitical issues. A divided Pakistan would not solve any of the problems the current nation has, and I wouldn't be surprised if the successor states would be even more failed.