Some ideas

[dascandy]

A few ideas I'd had over the past 11 hours of gameplay:

I would add coal gassing; a device that takes coal and hot water and turns it into flammable gas.
Flammable gas then is passed to a blast furnace that does what a furnace does, but quicker. It also is now the only way to create steel, by combining five iron plates with a lump of coal. It has two input spaces for that reason.
Flammable gas can also be put into a jet engine. This takes flammable gas and water as input and outputs high-pressure hot water - in essence, a very efficient boiler. Requires three pumps per engine to saturate.

I dislike the logistics robots. They remove the "how do I route this and get it somewhere" from the game entirely and replace it with fully automatic chests, together with "do whatever" thingies where there's no downside.

More intelligent creepers. Right now they pretty much "are". They don't have a reason to be where they are, they don't really have a thing to do there, they don't do anything but attack you in idiotically large waves and kill themselves on your turrets. They should have more of a reason to be - their own small mining bases, their own factories (albeit very small) and their own guns. They should have some "armored" versions that are much harder to kill. They should also have less bases, but better defended ones at that.

Where do the creepers get their "alien technology" thingies? This to me seems like a logical thing - find out where they got what you find there and go there instead. Finding out that it's nearly impossible to extract is fine; at least it has an origin. I'd suggest adding a pink rock type that requires a special mining device that then outputs one every 1200 seconds. Also, pink rocks are pretty rare and quite a few are taken over by the aliens who have their mining bases there (also explaining what they're doing there). That immediately explains why they guard them - they take a lot of effort to extract.

Creepers should go and steal from your belts. They can now run through your factory and ignore most of the things unless its in their way. They should actively try to disrupt your factory so that defending it is more important. Right now you can (see also TheZemalf's playthrough early bits, ep 3 or so) just put some gun turrets in the middle and go there when they come again.

There should be a "sandbox" game variant where creepers aren't as important - say, you start with 10x the health and regen a lot quicker. This would allow people who like just to do the "sim" bit to only play that with little impact from creepers - but just enough to keep the gun production relevant. Perhaps you could also add a "kids-safe" variant that has no health and no creepers at all. Could just be a difficulty rating, really.

[Pinkishu]

A few ideas I'd had over the past 11 hours of gameplay:
More intelligent creepers. Right now they pretty much "are". They don't have a reason to be where they are, they don't really have a thing to do there, they don't do anything but attack you in idiotically large waves and kill themselves on your turrets. They should have more of a reason to be - their own small mining bases, their own factories (albeit very small) and their own guns. They should have some "armored" versions that are much harder to kill. They should also have less bases, but better defended ones at that.

Creepers should go and steal from your belts. They can now run through your factory and ignore most of the things unless its in their way. They should actively try to disrupt your factory so that defending it is more important. Right now you can (see also TheZemalf's playthrough early bits, ep 3 or so) just put some gun turrets in the middle and go there when they come again.

I agree with making them more intelligent and maybe having them build bases, imo it would just be an uncessary PITA if they stole ressources and such, since you'd have to stick turrets all around your base, which also means you have to run conveyor belts all around it to auto-fill all those turrets, etc, kinda of annoying imo

[Nemoder]

If/when walls are introduced you likely wouldn't need so many turrets.

[MF-]

Where do the creepers get their "alien technology" thingies? This to me seems like a logical thing - find out where they got what you find there and go there instead. Finding out that it's nearly impossible to extract is fine; at least it has an origin. I'd suggest adding a pink rock type that requires a special mining device that then outputs one every 1200 seconds. Also, pink rocks are pretty rare and quite a few are taken over by the aliens who have their mining bases there (also explaining what they're doing there). That immediately explains why they guard them - they take a lot of effort to extract.

It's really hard to keep track of all my replies to all your paragraphs.
I know it would look like clutter, but you could have split this into 3 smaller threads by a suggestion category.

Alien artifacts are pink orbs because that is (IDK why) the best match for something unknown and strange.
I doubt they are literary pink or round.

[Blackmoor]

There should be a "sandbox" game variant where creepers aren't as important - say, you start with 10x the health and regen a lot quicker. This would allow people who like just to do the "sim" bit to only play that with little impact from creepers - but just enough to keep the gun production relevant. Perhaps you could also add a "kids-safe" variant that has no health and no creepers at all. Could just be a difficulty rating, really.

There already is the game Editor which allows you to create a sandbox environment and play your own custom scenario. As the game progresses there will be more options in the Editor as well. But at this stage your idea could very well be implemented using the current Editor.