TL;DR
I will be suggesting a parallel underground world, a new layer of the world as it is.What ?
My suggestion is to have a parallel world, underground to be explored.An underground world, where there may be grottos, infested with aliens, new ones and existing, and also more resources.
Drills may be needed to make new tunnels, and above ground passages.
Explosives will have new means of clearing a cave out, and landfill to cover up a cave entrance or tunnel.
Why ?
This will add a whole new aspect to factorio, not put it on a new path, but expand it vastly.Giving the ability to create more flexible constructions, and have a new world to explore.
A lot of things we create already, will be of great valuable, like lamps or explosives.
I want to keep this suggestion short, and if someone have similar ideas, or this gives you new ideas, you are very well welcome to discuss this topic here.