Indo-Aryans were an Indo-Iranian people who split off from the Andronavo culture and ventured in two different directions getting mixed in the East(India/Vedic Aryans) and loosing language and culture in the West(Mitanni). Now in this AHC,you need to have the Indo-Aryans in their original and unmixed form( They looked Somewhat Central to Northern European as per archeology of Andronavo) to have a good amount of population and their own country/province of a significant size. You can choose any region from the lands of the erstwhile Andronavo culture to Eastern Europe or even Western Europe. Their language should be close to Sanskrit and other Aryan languages and preferably remain Pagan to the modern era too.
How would this affect various developments between the two Indo Aryan peoples take place in the Modern era and especially Colonial era? They would be linguistically and culturally close to Indians and Racially and genetically to the British and Germans,Slavs,etc. How would this unique event affect the various developments? What if these Indo-Aryans people are befriended by the European colonialists to act as a friending agent with Indians? How would Indian social structure change in this ATL? How would Hinduism look in the modern era?
Conditions:
Language: Indo-Aryan languages only.
Genetics: Mix of Indo-Iranian/or Eastern European(both R1a) and Caucasian peoples with some traces of Uralic mixture.
Appearence: European(work out yourself based on various combinations of mixes of the above).
Religion: Vedic Paganism without becoming like Classical and Modern Hinduism.
Population: Modern day 40-50 million.
Country range: Choose anything between Slovenia and Kashmir with appropriate size,resources and society to build a modernized European country.
This is an ATL experiment for an evolution of the Hindu society and not anything related to replace populations or lighten anyone.