TL;DR
Modules are eternal, and often not used until late game.Why not use it's slots to other purposes?
What ?
New items, that can be fitted into module slot, and works as modules (it may be internally a modded module) but disappears after xxxx machine cycles.If used once, it can not be removed (it should vanish if user tries to remove it from slot, to avoid cheating. Or returned, but impossible to insert "used" bits again)
Crude Examples (numbers are just random):
Steel Drill Bits/Knives, that fits only into Electric Drill Machines. Works for eg. few thousands cycles and increase speed by 15%.
Negative effects are increased pollution, but not power usage. Of course, constant production of drills require energy and materials, as well as delivering it to outpost and replacing used ones with bots or by hand. And of course You may use one module less than normal.
Drills can have multiple tiers.
Tier #1: 5x iron plate.
Tier #2: 5x iron plate + Tier 1 Drill Bit.
Tier #3: 5x iron plate + Acid + Tier 2 Drill Bit. (Acid is used in steel production, see Damascus_steel)
Drill Bit cycles may be randomized (eg. 8000 +/- 20%) to avoid sudden need of replacing everyone at once by bots.
Furnace filters - works exactly as above, but fits only into furnaces.
Reduce pollution generated by furnace, with no speed reduction.
Assembler Mk1 CNC Pack
(Originally, I planned it as a separate idea/suggestion, to make Mk1 Assemblers somehow useful after first 30 minutes of gameplay)
Fits only in Mark 1 Assembler. Greatly increase speed of operation for one ingredient recipes only (should be as fast as Mark 3, or even faster) but increases energy consumption.
Then, Assemblers Mk1 will be useful in late game for making gears, wires, sticks and similar items. 2 ingredients recipes are not affected and do not consume CNC. (You do not change recipe to often anyway...)
Recipes similar to Drill Bits. With Tier #3 CNC Packs, Assembler may require access to lubricant to operate with full speed.
Similar devices may be designed for other buildings, as Assemblers, Raffineries and Chemical Plants.
Why ?
It adds more option to control various aspects of Your factory and adds some new logistic chains, also in early game.In early game, it will change furnace columns designs, if Drills should be inserted automatically (but, such early drills may be produced quickly "at the spot" by simple assembler, directly from plates), so all You need is one additional belt line between columns. In optional game mode, default Drills speed may be reduced without inserting drill, and "back to normal" with Tier #1, same thing for furnace pollution.
Optionaly, this devices may use dedicated slots in machine, to allow use in early devices (eg. steel furnaces), or such furnaces may have 1 module slot added.