Leaderboard (or at bronze/silver/gold stars) for most efficient designs
I think the game lends itself well to something like the Zachtronics games where you are given the goal of building a specific module (such as the ones already in the game as a starting point) and then challenged to build them with the fewest operators, or least space used to reach a specified throughput goal. It could also serve as a blueprint development lab where you can then take your best blueprints and use them in the main game. It doesnt seem like it would take much to add it from everything that is already in the game. just a new mode like creative mode but with a single island (or maybe up to 4 depending on the challenge), the leaderboard mechanism, and maybe a the ability to store more blueprints. to start , you could even forget the leaderboard and just gave bronze/silver/gold achievement levels. I would also extend the challenge to the module sets (most efficient design to feed blue 1 blue core, or 4 blue cores), and then as a more advanced challenge multi-building supply chains (core to proc to shard)