Here’s the problem-— Al-Sistani is closing in on his 90’s, the question is WHO will replace him when he’s gone?
Will it be someone like him? Or someone more akin to the Iranian Ayatollah?
The opinion of the Shia community in Najaf is that Wilayat al-Faqih, https://en.wikipedia.org/wiki/Guardianship_of_the_Islamic_Jurist i.e. the Khomeini version of how to run a country with a supreme leader on the top of the heap is wrong.
Iran has several times tried to push Najaf/Karbala to change this and even tried to push for https://en.wikipedia.org/wiki/Mahmoud_Hashemi_Shahroudi as a replacement (He died 2018 only 70 years old)
According to an article in 2018 by the Kurdistan Conflict and Crisis Research Center there are some possible replacements: https://en.wikipedia.org/wiki/Muhammad_Saeed_al-Hakim ,
https://en.wikipedia.org/wiki/Bashir_al-Najafi
and https://en.wikipedia.org/wiki/Muhammad_al-Fayadh
http://www.kurdistanc.com/EN/details.aspx?jimare=1050
I have not investigated this enough to give an educated guess. But it is probably important to check who Sheikh Abdul Mahdi al-Karbalai, the spokesperson for Sistani is spending time with.