Dev Journal #3 is up. Brad gives us a somewhat closer look at Colonies and Core Worlds, and how they'll function in the game.
I really like the concept that newly-colonized planets will automatically default to "Colony" status -- where you don't personally mange/govern it, but instead it simply feeds resources to the nearest Core World. I suspect it might take a little getting used to at first, but not overly much.
Turning a Colony into a Core World is an conscious decision you'll have to deliberately choose to make, and will require you to "sacrifice" one of your precious leaders (in order to turn them into a Governor). While you "lose" that leader, you've also now gained a Core World that is likely to be far more productive than the Colonies feeding resources to it.
The player also needs to be careful about not having too many Colonies feeding a single Core World: While doing so would give that Core World an immense amount of resources, and make it extremely productive (and powerful), it's also going to test your Governor's loyalty. The more Colonies feeding a Core World, the more likely that Core World's governor is going to be tempted to break away and form their own empire.
Thus, a balance needs to be maintained: You still need the vast majority of your planets to remain Colonies, but you don't want too high a ratio of Colonies/Core Worlds, lest you spark rebellion and/or civil war.