While the new terraforming system is being worked on, I have to muse a bit about hive worlds as currently implemented. Hive worlds are... surprisingly limited in the actual increase in population capacity they offer, while maintaining a high fertility. Now, having hive worlds that actually were far and away the densest possible worlds would, as things stand, be a problem, considering that Ashdar Prime and a few randomly generated worlds (including the Scavenger homeworld) are Hives. The high fertility is odd, given the ecological devastation supposed to be wrought by supporting the hive cities. There could be a *potential* solution to both these issues, if we take all hives that exist at game start as 'ruined' hives, basically being arid worlds with the ruins of old hive cities that can only be restored to a limited fashion. We can assume a local biosphere was left behind from the limited biological samples actually resident in the cities themselves. If 'true' hives were limited to the very late game, with Ashdar Prime only to be restored to having fully-functional hive cities when the technology is redeveloped to create them- and, in the process, devastating the biosphere outside the city walls- perhaps hive worlds would be more satisfyingly implemented.
All this said, I still love this game and its general approach to planetary environments and biomes- it's probably the best approach I've seen in a space 4X.