Anything IE is extremely unlikely as a language for the Indus seals; it only really fits with an out of India model of Indo-European, which is outright rejected by all serious scholars AFAIK. If we're going to look for contemporary relatives of the Indus language, the serious candidate is Dravidian. The Dravidian family was in India around the right time, and was definitely spoken in a larger area prior to the Aryan invasions.