Factorio Forums

Here's an idea to play with, assuming it's possible.

Alien assemblers spawn only within alien bases and cannot be built by the player (themselves or in any machine). These are the only places where you can assemble items that currently require alien artifacts.

There are several potentially interesting gameplay implications:
Assaulting bases must be done more carefully to avoid destroying the assemblers.
Choosing to play with smaller or more sparser bases means you will have less alien assemblers available.
More uses for trains as you don't want to ship the expensive items that will be used and made in these things on belts.
Random alien assembler positioning may require getting creative with belt and inserter layout.

This may need some tweaking of recipes to make it interesting. I don't know how the aliens will feel about us commandeering their bases. Massive pollution perhaps?

For an even sillier variation, replace all biter bases with various types of normal assemblers, and try and construct a factory using only those!