I was reading a History of India by Michael Edwardes. It says that by 600 B.C., the northwest had been closed off to invaders. It made me wonder about migrations up to this period. I only know about the Aryan migrations c. 1100. I've read about a few non vedic people in Northwestern and Western India, but didn't keep track. Some might have been located along the edge of the Himalayas, as if they squeezed in along this path. Witzel and a few others questioned if the Sakya of Guatama Buddah were Saka. This was due to their cousin marriage, which Hindus didn't do, their location and their large mounds. What do we know about later iron age migrations into India? Let's say from 1000-600, with an emphasis on the later period.
Edit: I found one of the references to a non vedic tribe. I'm not implying they were newcomers, but it is interesting: "The Kurus declined after being defeated by the non-Vedic Salva tribe, and the center of Vedic culture shifted east, into the Panchala realm, in Uttar Pradesh (Witzel, 1995)." Kuru Kingdom, Wikipedia
I found out that the Kambojas made it all the way to Cambodia, which is named after them. This was in a different time period, though.