Sorry to bump a 2 week old post but I just want to say that I personally would love to see this. I also want to say that if anything, I would suggest making the mac version an add-on library so you don't bulk the iOS version of sparrow up. Of course, if you can find a way to not bulk up the framework considerably then sure, why not. Then there are always going to be people that aren't interested in porting to a mac and don't want to bulk up the game at all for code they won't use.
So yeah, I really do think it'll be smart to go with the add-on route. I don't know if you decided on anything but that's just my 2 cents.