> Having another "non-limited, but not infinite" mode for stackable objects seemed to be strange, too.

I think having one library for "small stacks" and one library for "large stacks" seems more weird. Why not just increase the limit of 999 objects? Worst case, just limit the display to 999 but allow larger stacks internally.

> You can put oil into it, but then you would not be able to put any water into it (as a reserve) until the oil is used up

Why is that? If the liquids are objects, you can have a stacked water object and a stacked oil object both sitting in the foundry.

>  This is somewhat hindered by the fact that the producer handles fuel and liquid completely different from normal components.

I thought the whole idea of the "liquids are objects"-change was to unify this interface. I.e.: Remove the special handling of liquids from the producer library.

> - what is the benefit of having, say 100 water items in the kitchen, instead of a barrel that contains 100 water?

You do not need to route stuff through the barrel. You just look for components directly in the producer.

> - would barrel empty into the kitchen if you transfer a water barrel to the kitchen, leaving the empty barrel in the Clonk?

Yes, just like earth in the foundry right now.