In short, I'd like to see one or both of the advanced splitters to have an overflow option and new building that destroys whatever is fed into it.
I seen one post that talks about the overflow a bit, but has a lot of other things mixed into it too, so I chose to make this one to have just the overflow issue highlighted and the connected item disposal.
This issue came up early in the "Let's do something clever" stage of my experience, after getting the basics done very efficient. I found the first alternate recepies and that suddenly changed my needs for iron rods and plates, more of one, less of the other. So I came up with an idea of a smart factory. Feed in iron, then setup constructors that feed into a central bus and at the end, sort the bus (which I did per level of the factory, had 4 levels of it at the end). So if my needs change, I can just flip some constructors from one to the other item, and the rest would work just fine.
That of course works until one of the item outputs back up. As a simplified example: Two constructors, one makes plates, one rods, both merge into one output. Smart/programmable splitter goes into two storages, rods is full, plates not, belt to the splitter is filled pretty evenly mixed with both. Now the splitter stops because the rods belt will back up into the splitter, and it will no longer output plates, even if that storage is empty.
So a sensible step would be to have an overflow setting, which would take an item it cannot sort, even though it has a specific port for it, and dump it into the overflow port. There you could have large storage for overflows or the second part of this suggestion.
So while having the overflow is fine, there is then a problem, what to do with the overflow items, as they will just accumulate somewhere else until that backs up. So that's where a shredder would be interesting.
Building Suggestion: Molecular Deconstructor
Has one input, a smallish size (8x8 would fit well) and uses a medium to large amount of power while deconstructing. It has an item/min deconstructon rate (slowish, perhaps 10-20/min) which can be overclocked. It only can handle one item at a time (no stacks or buffer internal) and doesn't require configuration, it just destroys whatever is fed into it.
This could also be useful for getting rid of Nuclear waste. As such it could be on tier 7 or tier 8, or even tier 9+ so players have to struggle with the nuclear waste issue for a while before getting a solution to it. If nuclear waste has another method already pegged for handling it long term, then this could be a much lower tier item, around the same level as the smart splitter.