I thought I was done with Minecraft, but while I was in Prague last month Sara and I played a lot of it, and I realized that Factorio can't completely replace it, after all. In Minecraft there's always caves and abandoned mines to explore and new hideouts to be built as you do so. There's always vegetables to be harvested and re-planted. There's decorating around the house to be done. There's forests and pretty flowers that actually serve a purpose. Those seem to be the things that Sara and I both find lacking in Factorio. You could solve some of these issues with mods. But then you need to make mods. And though you could fake some interesting topology using portals and multiple surfaces (there are mods that do this, such as Subsurfaces and Factorissimo), you're always going to be missing the 3-Dness of Minecraft, which is a big part of why building stuff in it is fun.

On the flip side, Minecraft isn't designed for building giant automatic factories. (1) There's nothing that would require a giant automatic factory to build, and (2) machines always seem a bit hacky. Especially very expansive ones, since parts of them might be in unloaded chunks and won't reliably work. For example, I once tried to build an automatically switched railroad that would take me to a remote part of the world, but in order to propagate a single redstone signal I would have had to have my minecart run over pressure plates to force updates. For sending signals long distances, the unpredictable timing and requirement that a player travel with the signal makes sending bits serially impossible, so you need as many redstone wires as bits in your signal, which is completely unscaleable. Don't even think about trying to transmit signals through remote chunks that will never be loaded because a player never happens to come near it!

And then there's some features I'd like that neither game has:

• The ability to design unique objects out of other objects. For example in Factorio I might like to make a combined conveyor belt/pipe/railroad track/cable. In Minecraft I often want to subdivide blocks, e.g. take a piece of stone and carve something into it, or make steps out of something that the developers didn't make a step version of.
• In-game networkable computers that aren't built out of individual gates. For Minecraft I think there was a computer mod that did this, and it would probably not be difficult to do this with a Factorio mod (Zachtronics' games are all about this kind of thing but I'm not convinced that those games are actually fun. When I tried to play Shenzhen I/O I spent most of my time playing Solitaire).
• Portals to the other simulations or the outside world. I don't expect that this would do anything to make a 'fun game', but I think it's a neat idea and could be fun to play with, and might make the game more useful as a simulation or as a way to prototype manufacturing processes or data flows.

As I've mentioned before I seem to have some obsession with merging fun things with useful things and making my simulations networkable. Like, I guess I want to make building useful stuff more fun, and then I want it to be as useful as possible. The artist in me says 'make all your processey stuff into [simulated] physical objects so you can arrange them nicely and decorate them with flowers'.

And towards the end of making a thing that's as useful as possible, I'm thinking of building a system for designing objects made out of other objects. It could then take your specifications and generate Factorio or Minecraft mods complete with recipes and graphics. Or export to a path tracer to make pretty pictures. Maybe Appleseed. But you'd be able to use it to model realistic construction, too. Start with some 2x4s and drill holes in them and bolt them together to build a shelf and see how it looks before you build the shelf. There are probably tools to do similar things already, but I want all these things to integrate with my network simulator so I can turn virtual LEDs on and off with OSC packets, too.

In the meantime, have fun with this crappy smelter simulator: