The case will be settled through sharia law even if the parties can't agree.
That provision sounds very close to Christian biblical principles for resolving a dispute.
1 Corinthians 6
Lawsuits Among Believers
1 If any of you has a dispute with another, do you dare to take it before the ungodly for judgment instead of before the Lords people? 2 Or do you not know that the Lords people will judge the world? And if you are to judge the world, are you not competent to judge trivial cases? 3 Do you not know that we will judge angels? How much more the things of this life! 4 Therefore, if you have disputes about such matters, do you ask for a ruling from those whose way of life is scorned in the church? 5 I say this to shame you. Is it possible that there is nobody among you wise enough to judge a dispute between believers? 6 But instead, one brother takes another to courtand this in front of unbelievers!
7 The very fact that you have lawsuits among you means you have been completely defeated already. Why not rather be wronged? Why not rather be cheated? 8 Instead, you yourselves cheat and do wrong, and you do this to your brothers and sisters. 9 Or do you not know that wrongdoers will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor men who have sex with men[a] 10 nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God. 11 And that is what some of you were. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God.
So, according to that document and the comments regarding choice of law, we will have to begin electing and/or appointing islamic judges as more and more parties are allowed to use sharia law in contracts. It is then a short step to using sharia law in other matters. I think this is a very bad thing. There seems to be a flaw in contract law if the parties can select which set of laws they want to use and those laws can be from foreign courts. This is contrary to the intent of the Founders in avoiding foreign entanglements.