My idea is different than jtakemann's, which has a similar name.  I would like to see a population management menu that is more in-depth.  When I click on a race in my empire, I should be able to see the planets that their on, the planets that they would do well on, and the planets they would thrive on.  Furthermore, I think population growth and happiness should not only be dependent on food, access the luxury resources, and tech, but also include environment.  For instance, Sophons should have a penalty to growth if they are populating a Lava, Desert, or Arid world, but gain benefits on Artic, Tundra, Snow, and Ice.  Also, species may be more or less adaptive to hostile environs.  One could say that technology overcomes the discomforts on the environment, but I think the less tech you need to be comfortable, the more happy the population would be.  Finally, this would also benefit the player with migrations.  We would be able to see which planets would be best for the segments of out population, and as the empires grow, incoporating more planets and more species, we'll be better able to see what kinds of planets we need to take or terraform for our populations to benefit.  Right now, I have to manually cycle through, and write down on pen and paper which planets need which kinds of populations for max exploitation.