It is true it is hard to imagine the Watchtower Society allowing outside historians to consult their archives in New York. But I think it is interesting that they have allowed some historians in Germany to access their archives in that country. The Watchtower Society must have calculated that the benefit from helping academics to write about and thus promote their history during the Third Reich was worth any risk involved. It is hard to imagine any similar benefit would result from opening their archives in the United States to outside researchers, so it remains unlikely.
The Watchtower Society has been equivocal about outside research of their movement in recent years. On the one hand Witness lawyer Carolyn Wah wrote an article in the Review of Religious Research encouraging/advising researchers how to go about studying Jehovah's Witnesses, while at the same time the Service Department has been sending out letters telling elders not to cooperate with researchers. It seems as if the left hand does not know what the right hand is doing, or there are significant differences of opinion over what approach should be adopted at the headquarters.
But those contradictions having been acknowledged, as a generalisation I think it still may be fair to say that the Watchtower Society has become more open to academic research of the movement in recent years. Bethelites such as Jolene Chu and Johannes Wrobel have been encouraged to write articles for academic journals on Watchtower history; they have allowed outside researchers to consult their archives in Germany; and representatives of the Watchtower Society have taken part in conferences alongside academic historians. The knee-jerk responses of the notoriously reactionary Service Department notwithstanding those are significant developments in their own right.