I came to realise that currently there are a load of blocks in Minecraft, and there are a load more to come.
Furthermore, it gets more and more complicated to sort those items automatically - and there are many items that i do not necessarily want to have in separate chests (like differently coloured wools for example).
So here is my suggestion. Hoppers should always try to transfer the one item it has most of it inside. Just instead of taking the item on the most left, pick the one with the most items.
In this case it would first pass on the white wool, until its equal to the pink one. Then it would reduce both down to match the others.
This is a small change, but would improve the usability of the hopper drastically. You could, with a single hopper, sort 5 items at once with the usual "Hopper-Item-Sorter".
This would then be the default state of the current Sorter with the "Overflow-proof sorter" design (displayed below). The hopper only excepts the 5 kinds of wools in the hopper, but all 5 of them! And if you want to just transfer one item, you can still put some junk in it, as a buffer.
The great thing about this is it would not change any current game mechanics. Any current Redstone sorter would still work as intended, but this would greatly improve and simplify future item sorters - especially with the loads of slabs, stairs, etc incoming!
And in my opinion it does not make the sorter kinda "overpowered". You still need to have some know-how in order to make it work properly.
I hope you see this and consider it.
Kind regards. :)
PS: If the item count inside the hopper would be increased to 8 instead of 5, you could sort out all 16 coloured blocks with just two hoppers. ;)