About the coding part: how do manufacturing requirements work, anyway? Is it possible to have a manufacture that uses an item other than alloys or elerium as a "material"? If it's not possible yet, I think we should add it. Think about weapon improvements: using a plasma rifle and an advanced scope to manufacture a plasma sniper rifle... or a mod that only allows use of alien weapon after "modifying" them for human use... endless possibilities
EDIT: hmmm... looking at the ruleset, the manufacture part lists "requiredItems: ... ". I guess you can list anything here, right? so it should be perfectly possible to create a "fusion cell" item that can be manufactured with "requiredItems: STR_PLASMA_PISTOL: 1".
I don't know if it would also possible to make elerium able to be manufactured from several other items, though... like having multiple "Elerium" items in the "manufacture" category with different requirements (one with requiredItems: plasma pistol clip, one with requiredItems: plasma rifle clip and so on)... probably not.
EDIT 2: okay, yes, it is absolutely possible to have an item require any other item for manufacture. I just quickly changed the Laser Rifle to need a Laser Pistol for manufacture, and it works just fine.
EDIT 3: okay, and it is perfectly possible adding a manufacturable Elerium that requires for example a Plasma Pistol Clip. So it should be perfectly possible to create small/medium/large "Fusion Cell" items that can be "extracted" from the Plasma Pistol/Rifle/Heavy, and that are then raw materials for human weapons. if you put "UFO Components" as the item type for those Fusion Cells, you don't even need to create an image for them, as they will never appear in the battlefield.
however, it is not possible to have one item that can be "manufactured" in more than one way. so you couldn't make Elerium extractable from more than one item. too bad. I guess adding that functionality would require some code changes, possibly affecting the ruleset, too, because the "manufacture" entries would need to take into account that a manufacturing process has a name that differs from the end product (for example, the manufacture process would be "disassemble Plasma Pistol Clip", "Disassemble Plasma Rifle Clip" or "Disassemble Heavy Plasma" while the end product would be "Elerium 115"... which in turn would affect the language files...