If you have a hopper with a filter, what do you do with the non-filtered items? Leave them in the box? That would be very limited. Put them somewhere else? How, there is only one output on the hopper.
That's why we need a sorter. It's a hopper, but it has five outputs, N,S,E,W,down. Each slot has it's own filter, and the combination determines what the filter will suck in and put out.
If you don't filter, the hopper will use it's outputs to randomly fill connected containers using a random stack. While sucking in items, it will prefer items matching one of the incomplete stacks, just like the hopper.
Some containers may have natural filters, e.g. the furnace will only accept burnables and smeltables, limited to one stack each. If an output is unfiltered but connected to a furnace, the filter will not treat this output as filtered while choosing what to do, but it may fail to do anything there. In this case, the other outputs are tried.
If there is at least one filter, unfiltered outputs may not output this item. You may have two outputs with the same item. In this case, both outputs may output these items. Again, if putting the object fails, the other items and outputs are tried.
Each output can individually be disabled.
A filtered hopper/sorter cannot accept/suck in items if it's filters would not allow to get rid of them (output filter = input filter).
How to craft? It should be a modified hopper. I expect it's recipe to change, so there is no point in thinking about it yet, is there?
Always a point in thinking about a crafting recipe. It can't hurt and it makes your idea look bad. As for the actual idea, I'm iffy on it because I know Dinnerbone was against easy full automation and right now it is possible to sort items automatically, it's just rather expensive.
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I think a good crafting recipe would be 4 hoppers in a plus shape (1 input, 3 outputs), 4 comparators in the corners (for the logic, and also to detect how full the container is) and maybe a nether quartz block in the middle. The 2 side outputs are to the left and right when placed. It should also be larger than 1x1x1, as that will help limit it. As for how it would work, it would have a filter in each output like the OP said, however there should be 4 toggleable sorting modes. Exact mode, where it only sorts damage values of the blocks put into it; as an example, a grass block in the filter slot would only sort out grass blocks in Exact mode. The second mode, Narrow Association mode, sorts closely related items; that grass block in the filter slot will sort out grass, soil and mycelium blocks, or if you placed raw beef in the filter, it would only sort beef, steak and leather. The third, Broad Association mode would sort based on wider associations; the beef in that second slot would sort the previous beef, steak and leather, but also sort out all meat input into the sorter. The final mode is Systemic mode. Systemic mode sorts out all related items- the grass block would sort grass blocks, mycelium blocks, soil blocks, and anything that grows from them. That's my thoughts on the matter, sorry if it was long-winded.
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This suggestion reminds me a lot of the Diamond Transport Pipe, a la Buildcraft. I feel like making its structure be a bit more like that would be preferrable, but honestly, yeah. I'm all behind this concept.