It would not have to be a very ambitious mod. Just add a morale bonus to the farms in PlanetImprovements.xml.
It would not be Metaverse compatible, however.
I think you missed the part about freighters having to carry food to other worlds and selling food as a resource. That would NOT be an easy mod. And if they DID just add a morale bonus to farms this would wipe out the entire economic strategy; more farms would mean your population could expand with your morale INCREASING instead of DECREASING the whole time, meaning you could set HIGHER taxes, which would be COMPOUNDED by your now MASSIVE population, meaning you could afford anything you wanted, and still have a HUGE treasury. No, this simply wouldn't work.
I don't think the idea of freighters carrying food to worlds is very good either. I mean, when you think about it, EVERY mining starbase mines a resource, morale mines natural medicine, for example. I think it is automatically assumed that your resources of all kinds are always being distributed by transports, and that they are too trivial to be a serious target in war and would screw the graphics engine with so many ships.
What I think WOULD be a good idea is to set up a "food economy"; essentially you would consider food as a form of money, and your farms would produce food and add it to your "food treasury", and your population would consume food weekly, subtracting from your food treasury. You could trade excess food or buy extra food via the diplomacy screen. The population limit could simply be limited by the Planet Class (bigger planets can hold more people) and your overall population would be limited only by the total amount of food you produce. If your food treasury ever went negative there would be a morale penalty (which would inherently slow population growth), and if you went too far down people would start dying off. You could also have a limit cap to your food treasury (reasoning: food spoils and you lose wasted food), but they could have a technology branch that would increase your food limit, or maybe just add this effect to an existing tech. With this players could establish specialized farming worlds, and support their whole empire on a few worlds. Of course, this would allow for the possibility of a "galactic siege", as some of you mentioned, being able to capture enemy food worlds to starve them into submission.