Blueprints

Be able to save part of the factory, like a smelting setup, to a blueprint that can be then placed later. Ideally, blueprints could be saved globally and shareable to other players.

Really excited about this!

Please! Because people like me who aren’t very good at building clean, or perfect ratio use.

as in Factorio?

Yeh, id love to see a copy and paste feature also.

There's now an "area clone tool," aka copy/paste feature. Use the 'C' hotkey and drag select an area.

I like the new drag and select, but can it include pipes and conveyors too? If you only do the buildings (whilst appreciated, the connections are the real hassel.

Blueprints & Copy/Paste, definitely required.

I'd settle for my transport belts to just work with Copy/Paste

I love this idea, especially when my belts don't always go where I tell them!

Saveable blueprints (including belts and pipes)... exportable/importable blueprints is the basis of forming a community around this game.

Oh yeah... i love it at Factorio and Andrew is right... the ability of sharing Blueprints is a big step for communitys of those games.

please do this

My thoughts on how this could be handled:
You open up the "blueprint screen" which would basically be a massive blank scratchpad you can build on. The buildings wouldn't be planned, though, instead they'd be instantly built like in a creative mode. You could then add customizable nodes that will output/input desired amounts of items/ores/materials at specified rates so you can test your design live. Make sure your ratios are working correctly. Instead of nodes for resource generation, you could assign a storage to be the node, too.
Then from this screen you can save blueprint which would be added to a list of your saved blueprints.
You could also implement a "Copy to Clipboard" which gives you a text string of the blueprint for easy sharing on the community.
This would be a extremely useful tool for teaching and showcasing builds, as well.

Blueprints will break the game. Part of the attractiveness of the game is the puzzle solving aspect. Blueprints will completely remove this aspect, specially if there is an export /share feature. The copy paste feature is good enough. You can create small modules and copy/paste them as demand increases.
If people are able to share blueprints and basically paste an entire production line then what is the point of the game?

I don't think blueprints are game breakers. For me, they are a requirement for long gameplay. At the moment, I'm building large plants from individual machines. I pay attention to the efficiency but also to the design. And that is fiddly work. Therefore I want to save these blueprints to be able to load them on the next map. So I can adjust them there afterwards to the map size and further optimize. If I have to rebuild the construction of my partly large plants on every map, I won't be happy with COI for long.
Therefore, for me: Saveable blueprints are a must have.
For me, the implementation of these features would suffice as follows:
1. I build a plant from several machines, storages, conveyors and pipes.
2. A tool similar to the current Copy & Paste tool, which lets me mark the whole plant and save it under a name of my own choice.
3. A function on each map to load and edit these blueprints before building.
So I hope for a quick implementation of this feature by the devs.

Blueprints & Copy/Paste, definitely required.

As what Hydrogen said, I think that it would greatly take away from the game itself. There are definitely things that could be blueprinted, but at the present time there are very few that I would even think would be useful. A lot of the game is a puzzle, and getting things to fit into certain areas, and blueprints wouldn't be much help there. There are already a lot of youtube videos, and hi-res screenshots that show how things work already.
I guess if you want to be completely lazy, and just have someone build the game for you, I guess more power to you. Many people are just taking things that are absolute musts in game like factorio, and trying to shoehorn them into a brand new game.

It's simulation game, not a puzzle... You two so far can continue play it as puzzle without using saved blueprints... but this simulation is too involved to keep building ideal steel smelting setup (for example) from scratch whenever something goes wrong. Being able simply saving blueprints to avoid annoyingly repeatable tasks of building same basic setup over and over again will keep me playing this game, otherwise I'll just wait till it's implemented or forget all about it.
IMO, this game has a lot of potential if saving blueprint is an option.

I think allowing Blueprints as part of the Research tree would solve balancing considerations brought up by Hydrogen.
Having the ability to edit blueprints (possibly in a new Editor View, like Zaff suggested), then having blueprints available (either through sharing as files, or possibly steam workshop later on) both in sandbox mode by default, or gates behind e.g. Research 2, and then allow selection of blueprints based on the completed research (e.g. you cannot select a blueprint that uses Storage II, when you dont have it researched)