John Peterson (2017) suggests that "pre-Munda" ("proto-" in regular terminology) languages may have once dominated the eastern Indo-Gangetic Plain, and were then absorbed by Indo-Aryan languages at an early date as Indo-Aryan spread east.
dʒˈɑːn pˈiːɾɚsən tˈuː θˈaʊzənd sˈɛvəntˌiːn sədʒˈɛsts ðˈæt "pɹˈiːmˈʌndə""pɹˈoʊɾoʊ" ɪn ɹˈɛɡjʊlɚ tˌɜːmɪnˈɑːlədʒi lˈæŋɡwɪdʒᵻz mˌeɪhɐv wˈʌns dˈɑːmᵻnˌeɪɾᵻd ðɪ ˈiːstɚn ˈɪndoʊɡændʒˈɛɾɪk plˈeɪn, ænd wɜː ðˈɛn ɐbsˈoːɹbd baɪ ˈɪndoʊˈɑːɹɹɪən lˈæŋɡwɪdʒᵻz æɾ ɐn ˈɜːli dˈeɪt æz ˈɪndoʊˈɑːɹɹɪən spɹˈɛd ˈiːst.