Some kind of penalty should exist, even if it's just something like a linear growth of strategic and luxury resources required to sustain the population.
Always felt a food mechanic is lacking in DW though, which is closely tied to this. You can blockade a world of 15 billion people and nothing really changes. With food introduced it changes so many mechanics of the game.
Dream Idea pitch here, bare with me.
The food production of a planet dependent on type, quality, size and population. Continental, ocean and marsh planets obviously would produce more food than ice, volcanic and desert ones.
Depending on size and quality an output modifier is applied on the base food production of a planet. As the population of the planet increases, the needs might outgrow the production of food, and the empire need to find new worlds to colonize/conquer to secure the food supply.
Would give a reason to limit population growth on colonies etc.
As not to make this unbalanced on different starting planet types. Humans who start on a better world might require maybe 1 unit of food per 1 million people. Teekan's who are much smaller, require maybe only 0.5 units per 1 million people. I think I can make a case for most of the races on non-temperate worlds needing less food except for the Mortalen and Naxxilians.
If you don't have enough food for your colonies there would obviously be unrest and riots. As famine becomes an actual thing maybe it could be simulated by a plague that kills the pop until it's close enough to the food threshold required to sustain the population.
Food doesn't have to be an actual resource shipped around by transports. Could as well just be some hidden number on worlds controlling it's growth etc.
Sorry for the poorly formatted rant. A man can dream ¯\_(ツ)_/¯
< Message edited by Kingah -- 9/24/2020 2:54:52 PM >