My ideas list for interesting Factorio challenges (apropos of nothing):
- Products with a shelf life (must be consumed within 15 minutes or it turns into a "waste" product)
- Products with "refrigeration" (e.g. an item which must not exist outside of a temperature-controlled chest for more than 5 minutes at a time)
- Catalyst ingredients with a chance of being consumed (presently emulated with probabilistic outputs, native support could be interesting, the catalyst would just sit in the machine until it was consumed)
- Mining ships (an entire factory moves to a location and extracts resources). The screenshot seems to imply that some kind of spaceship will exist, perhaps this is coming.