As all of you, I love Factorio a lot! Also, I was thinking of making a game that starts from the same basic concept (assembling items), but you can also build a city and have to manage it. Transportation will also play a big part: there will be ATUs (Automated Transporter Units = small robots), automatized trains and space ships. Also, the fighting will be much more developed, there will be separate missions where you will build Attack Robots and fight the enemy factions.
Here is a small concept of a building:

What do you guys think?