Additionally to the above answer, other social movements within Hindu religion have also advocated and practised Dalit preists in past too:
Arya Samaj : Swami Dayanand, Arya Samaj and his contribution in Dalit Upliftment ( ref: http://www.aryasamaj.com/enews/2015/apr/7.htm )
Shahu’s other initiatives included restricting child marriage in his state and the encouragement of intercaste marriage and widow remarriage. He long patronized the satya shodhak samaj but later moved towards the Aryasamaj. Under the influence of these social-reform movements, Sahu arranged for several non-Brahmin youths to be trained to function as priests, in defiance of timeless convention which reserved the priesthood for those of the Brahmin caste. However, he faced opposition from many, including Lokamanya Bal Gangadhar Tilak , the very famous patriot of that time. In 1911 a thread giving ceremony was performed among Vashisht, a Dalit community in khairpur, nathamshah in Sind.
also related links are:
- Examples of Varna migration in Hindu mythology?
Examples of Varna migration in Hindu mythology?
- Can a person change his caste in Hinduism?
Can a person change his caste in Hinduism?
- Can a Sudra become a Brahmin in 'this' birth?
Can a Sudra become a Brahmin in 'this' birth?
- https://hinduism.stackexchange.com/a/24623/13287
https://hinduism.stackexchange.com/a/24623/13287
- temple where upper castes bow to Dalits Priests since 200 years
temple where upper castes bow to Dalits Priests since 200 years https://www.hindustantimes.com/lucknow/a-temple-where-upper-castes-bow-to-dalits/story-Qbl3vPUXX53GxP9UyPBjfO.html
https://www.hindustantimes.com/lucknow/a-temple-where-upper-castes-bow-to-dalits/story-Qbl3vPUXX53GxP9UyPBjfO.html temple where only married Dalit women are priestesses, and also males can not touch the idols. This temple is even more older than 400+ years.
--- https://hinduism.stackexchange.com/a/26204/13287