Until a bilingual of some sort is found, or an archive of longer texts, probably little headway will be made. Most of those working in the field (that is, not politically motivated non-scholars) agree that the language preserved in the script was agglutinative, but efforts to make it out as an archaic version of Dravidian have failed (and the oldest surviving Dravidian texts are over 1000 years old, that includes some from a Roman-era Red Sea pottery factory); similarly, no one has made Sumerian fit it either.
It’s known to be a writing system, as there’s actually a surviving “welcome to [town name]” type of sign outside one of the old Harappan city sites, but longer texts are mostly lacking, probably because they were originally made on materials which have not survived.
Since it was agglutinative, it could only be either Uralic or Dravidian (the others are too far away) - and since Sumerian and Elamite was agglutinative and these three were in contact with each other it's not too far fetched, in my opinion to construct a grand Elamo-Dravidian language tree.