Like I already said there is no issue here of whether all Madhahib would agree on on single law there are so many ways to deal with this with respect to all differences that might exist and which have always existed..
Saudi and Iran are enemies mainly for sectarian reasons and when Iran used to be allies with USA the Saudi-Iranian relationship were better than ever.. these weak and puppet regimes are not a good example to give nor am I saying that the Sunni and Shia should be forced into same set of rules.
As for sufi you do realize they are in most cases Sunni?
We have on one hand the Ash'ari and Maturidi and on another the Athari now in all these three Sunni schools of theologies you will find sufi tariqas/orders...
What you want to speak about is the Ash'ari-Salafi divide.
Your issue here though that you want to deal with it like we have reached a dead end and claim a complete understanding to it all and not like it is a ongoing thing that evolves and changes with times..
So again and again there are obvious differences in understandings but that is the case with any other world view let it be the secularist world view or any other world view!
The Western world were not always ahead of Islamic nations that is another BS statement you are making!
You can surely claim that today it is ahead but this is due to their current political stability and being a world power..
When the Muslim world was in that position of power it was ahead of the Western world too in terms of "development, innovation and standard of living". Shariah was never obstacle for any of this for many centuries so why should it be today!!
And there is not such thing as imposing 100% Shariah what is that even supposed to mean? You are again assuming that we have reached some sort of dead end of understanding Shariah and not something which is dynamic and constantly developing.. why in this case we still have fiqh!
What would even be the point of fiqh if would could reach the level of imposing 100% shariah!
And Like I told you earlier there are no issues in adopting laws that do not contradict the Quran and Sunna!
So you have to be more specific with which Byzantine laws were adopted and how they contradicted the Shariah.
Could you then tell me how this model would be any different from the Western European model of a typical Secular, liberal, nationalistic state?
And what if a very good number of people's choice was to adhere to the Shariah? How do we solve this problem then?
Not everybody is willing to let go of this so easily as you like to think!
Sufi is a sect (especially that a lot of sufis are considered heretics by people like ISIS and salafists) , Salafism is a political doctrine and not a religion. You don't know what you are talking about when you talk about religion. Religion is tradition and values that were compiled over the ages. Salafism imposes an intolerant rule that considers everyone infidels or heretics who don't abide by their doctrine. You are telling me that a Shia and a salafist will agree on a sharia law? nonsense.
My understanding is fine, you need to realize that religion is a very subjective realm and madahebs will not agree on each interpretations. You are too naive to think that they would agree on set of laws when there are so many differences. If Turkey one day imposes sharia law it will be very very different than the sharia law that is used in Saudi Arabia. Even Saudi Arabia's laws are different than UAE ones.
Like I told you, Fiqh will always expand Sharia, but you cannot even agree on Fiqh, as sects in Islam have different Fiqh and different Sunnas.
Let's make a poll in Lebanon shall we, who will adhere to Sharia between Sunnis and Shias, let's assume a sunni sharia vs a shia sharia and see the results. Let's also put into the mix forcing Christians to pay jizya and them being treated like second rated citizens who can't hold high public offices or be in the army in the mean time, let's see how many people in Lebanon would agree to that.
I stated the the ottomans used adaptations of Justinian and Theodosus codes for their "Qanun". What's also interesting the Umayads used "Diwan" Christian laws and relied on some Roman laws on certain matters, for example mostly on commercial matters.
People will get used secular laws that will provide them with a good life and improve their standard of living. Everyone will be equal under law. This is what Lebanon needs to govern 18 sects.