Are there any Mujtahid Imaams alive today who can challenge any of the rulings of the Four Imaams?

Answer

There are no Aimmah Mujtahideen alive today. In fact, since the past 13 centuries not a single one of the great Fuqaha and Ulama had challenged the illustrious four Imaams. Great Ulama, Mufassireen, Muhadditheen and Fuqaha such as Imaam Abu Yusuf, Imaam Muhammad, Imaam Sarakhsi, Imaam Raazi, Imaam Ghazaali, Imaam Bukhaari, Imaam Muslim and innumerable others all followed one of the Four Imaams, and no one challenged them. The one who did, deviated, e.g. Ibn Taimiyyah. The age of the Aimmah Mujtahideen terminated with the ending of Khairul Quroon (the three noblest eras of Islam) – the ages of the Sahaabah, Taabieen and Tab-e-Taabieen.

Now what you will find remaining today is the chaff. The Ulama-e-Haqq of this era will be the chaff. In relation to the great Fuqaha, i.e. the Muqallid Fuqaha, the true Ulama of this age are mere 'chaff' while the Ulama-e-Soo' – the evil worldly scholars – are ghutha (rubbish) who betray Allah Ta'ala, the Nabi, the Ummah and Islam for the miserable benefits of this world.