Should questions on pre-Islamic history (like, Did women in Arabian peninsula have "Hijab" before Islam?) be on-topic, unless their relevance is established by OP?
As I see it, there's two classes of "pre-Islamic history" that need to be recognized here:
This would refer to those customs and traditions that were practiced and/or commonly known and accepted during the time of the prophet. As he did not preach to a vacuum, the value of understanding the non-Islamic culture that he was actually preaching to cannot be dismissed, especially when dealing with jurisprudent methodologies that emphasise urf.
The example question in OP is (or probably should be) an example of this, as there would appear to be value in recognizing whether the practice of "hijab" is actually revelation versus it being a pre-Islamic custom that was simply condoned or co-opted.
Culture and history that was only relevant to generations before the the prophet is a different story altogether. This is not to say that such situations are never relevant to Islam or Islamic studies: In many cases, an historical event can still fall into the contemporary category because it was commonly known and accepted (e.g. the story of Ashaab-il Fil) or it can have clear Islamic relevance by being directly referenced in the Islamic literature (again e.g. the story of Ashaab-il Fil).
However, if the connection to Islamic study is not obvious, significantly more effort would need to be expended on the questioner's part to demonstrate on-topicness. Otherwise, such questions would almost inevitably be better suited to History.SE.