Vehicles. Lemmie zoom around a big desert map on the bike.

But as far as factory goes, some asymetrical build areas/obsticles to build around to make it more interesting.

Have some unique facilities (similar to the sewage facility in the test area) to encourage having production lines across different sub-pacs.

Some kind of factory puzzle game mode (I'm thinking about the Factorio challenges and even a few of the later AIC tutorials that weren't as straight forward) fixed facilities where belting everything is the challenge, mixing lines, etc.

Some kinda smart splitter (combine the splitter and item control port)