For a start, the Middle East board is not very active - but lots of questions about Israel on the Kosher board do have crossover interest with general audiences traveling/living in the area. Though I don't keep kosher, posts on new restaurants in Israel do occasionally appear on the kosher board - and definitely interest me. Also, posts such as good kosher restaurants for a large group with kids or best kosher items to buy in the shuk will have a lot of appeal to travelers/ residents even when the kosher part of the question isn't as relevant.
On the other hand, some questions that start on the Middle East/Africa board (i.e. Need recommendations for x type of kosher restaurant in Israel), might find a more informed and helpful audience on the Kosher board where there's more knowledge on various kosher specifics. Basically, I think a number of posts benefit both boards and would love to know if it's even possible for posts to have a shared posting/presence.