Use player driven activity milestones to trigger some side quests.

Some of the planned sets of side quests mentioned in the dev update could be triggered by reaching certain milestones in the various normal activities of play (IE - researching, exploration, raw material gathering, airship characteristics, etc.), rather than always stumbling across them environmentally. The point would be to reward the player-driven activity of exploring areas, gathering resources, researching new technologies, building out their airships, etc. with quest unlocks so that the player feels more connected to the game and to the environment as they proceed in post main game activities.