In the hopper UI there should be at least one area where an item can be placed and make the hopper ONLY pull that item. For the average user hopper sorting can simplify item organization and for the advanced user this can be used to build simplified versions of often complex machines such as a door lock with an item "key."
Yes, I realize this would obsolete some redstone used for sorting, however, item sorters are known to slow down servers. This change could possibly speed up servers by removing the lag from often massive redstone sorting machines. (Think Mumbo Jumbo sized).
If the wish is to make a separate hopper for sorting, perhaps a sorting hopper is crafted with redstone in some way, though I think it would be best on the regular hopper.