Feel free to chime in with ideas for mechanics or balance ideas.
Right now, I've got a couple of thoughts floating around for what would be fun, and fill a niche in the current gameplay.

-Soil Centrifuge (Processes soil much faster, possibly more efficiently. Small grid variant?)
-Stone Crusher (Produces crushed stone, which is faster to refine and more resource dense.)
-Gravel Processor (Haven't decided yet. Changes gravel into something more useful.)


More details:
The soil centrifuge would be a way to get resources out of soil fairly easily, including on a small grid. It would probably be pretty small, initially using the small grid H2/O2 generator model, and cheap to produce. The idea would be to make it workable to slap one on your starting drop-pod to make the very early game resource grind a bit easier. To that end, I think that I would also be further dropping the processing speed for the normal soil separation recipe, to encourage the use of the extra equipment.

For the stone crusher, I'm thinking that the crushed stone might also have trace levels of cobalt, gold, and silver depending on the type of stone. The idea is to incentivise the extra step. Ideally, crushing the stone first before refining it will take less total power. The ore crusher would be quite large, probably using the full refinery model at first. The niche it's supposed to fill is bulk stone processing when doing large mining operations. That way, your inventory won't get clogged up with useless "stone". I want people to enjoy working with the stone, in addition to ore, when they strip mine a huge area.

The gravel processor is one that I'm still undecided on. I like the Gravel Sifter mod, but the way that it produces trickles of every resource, including uranium and platinum leads to a gameplay loop where you are reluctant to go to space to get those resources, since you are getting very small amounts of them on earth, but it's slow enough to be frustrating. I think I would stick with converting gravel into iron, silicon, nickel, and magnesium ores, which you then need to refine like normal. It means you can dump excess gravel and have it still be useful, but it's not overpowered.

Another idea would be to make the gravel processor more like the survival kit, in that you need to queue up "recipes" for the refining to happen, and you could select what resource you want to refine for. This would mean that you could use gravel as a sort of catchall resource, making up for the shortfall of any other mundane resource. If I did it this way, I might go so far as to include the option of refining it down to gold or silver, at the cost of producing very little resources for the amount of gravel you put in.

The gravel processor would probably be based on the full assembler model.