::::Theory: there's an emerging binary here, created on both sides between Arabs and Jews, or if you like Palestinians and Jews. I have no idea what you mean by an identity "neither historically true nor universally common," and I think most students of nationalism would consider them socially constructed, often in opposition to other groups. That every binary opposition covers up people in an overlap is obvious, and Wikipedia should describe notable entities within these overlaps, including say, the Mizrahim. 
 ::::Practice: The facts that come out of these distinctions have dominated life in Israel/Palestine since the Mandate period, and cannot be ignored. If Palestinian refugee refers to non-Jewish Arab Palestinians (who have been treated differently by Israeli law as present absentees or as Arabs who cannot return to their homes), there are good historical reasons for that. That is the term is a product of a real history. Our job as editors is not to take apart verbal constructions to find missing components, but to provide encyclopedic content on entities described in reliable sources. 
 ::::If there are reliable sources discussing Mizrahi refugees from East Jerusalem etc., consider writing about them in Jewish exodus from Arab and Muslim countries, and branch out if space becomes a problem.