Back then, they had Jordanian citizenship. Since nobody's proposing to move them - they will remain in the same exact place they are now but will gain Palestinian citizenship in place of Israeli citizenship, and given that the Palestinians are keen not to have Jewish citizens in a new Palestinian state, what's wrong with just redrawing the boundary so that many of these Arabs who are not Jewish become Palestinian citizens? Makes all the sense in the world. You can't have two national narratives that are the exact opposite in one country.
UN aid chief says no warring parties observed Yemen truce (Reuters)
from the article: French peace plan would require Palestinian recognition of Jewish state