on one problem with the OIT hypothesis, which is the ornery case of Anatolian Indo-European, Hittie, Luwian, and Palaic. The pre-Anatolian Indo-Hittite at the source of these is one of the oldest either daughter languages of proto-Indo-European, or else a parallel older than this to archaic proto-Indo-European, sometime very early indeed, creating problems for the OIT.
Not being a close student of these issues, I say all this with some temerity, and remain open to the various hypotheses now current.