The problem with handling MiRV is limited to long distance exchanges. Russia/US are in a situation vis-a-vis each other wherein any missile launched from the other's territory cannot be intercepted before reentry, unless the defence system is close enough. American deployment of Patriot missiles in Europe was as much for European protection as for intercepting Russian launches early enough. Pakistan, however, is not in the same position. The maximum distance that it can launch its missiles from is around 1,000 km. Any BMD shield will obviously be calibrated to this scenario. The only realistic option for Pakistan would be to invade Iran and annex it, so that it can launch missiles from farther away.