Yep, but that honestly wouldn't be much of a problem. For example, if you use BC to pump items into the top a generator, they just have to be extracted from the generator. So if anyone has a problem with that, then...
I think Alb was talking about items with a recursion loop mechanic. For example, you can macerate ingots back to dust, and then heat it up to get the ingots back. In code, the "backwards" cost of an ingot would get stuck in an endless loop trying to negotiate the cost. There aren't many items that have recursions, and this was the most basic....but others include almost ALL of RP2 (especially the panels and subblocks).
However, EE already contains a "cost" of materials, so why not do the following:
1. Create a database with API hooks so that items could be added to the list (with an associated cost) and can be retrieved at any time
2. Ask Eloraam/SpaceToad to include it into Forge
3. Use it, and any items not in the list, cannot be a "valid" target for UU creation (maybe have a green/red light to show acceptance). So it leaves it up to the mod developers to add their items to the price list (which also relieves the burden on IC2 of checking if specific other mods are installed).
Also, when putting UUM into the "input" slot, the machine should accept it as added energy directly (the amount required to make UUM in the first place). Although UUM is not required (the machine _is_ creating matter), it helps in the same manner scrap does in a normal fab. However, this now makes this machine idea a Mass Copier....but I think it's one of the turned down machine ideas, can't remember.
The item pricing database could be general enough to allow mods that already have a pricing guide institute it without wasting memory on duplicate listings (Tale of Kingdoms and EqEx for example already do item prices). If created, there should be a cfg file so that the prices of the vMC items can be located and altered if player/admin feels the need to. Obviously there would be a conversion multiplier between the price of an item and the EU cost to fabricate it, but I figured it didn't need to be said...prices should just be basic values.