This would break many, many existing designs, so I'd rather not change it now.
What about clicking on the sort block changes it's direction of flow? Or perhaps a "Sorter Alt" block that can be built with this behavior.
It is super weird to separate multiple materials from one production line. You end up with a ton of spaghetti messes trying to separate it all out. I pretty much avoid using them except for emergency situations where I need to incinerate a resource that infected a conveyor belt.
EDIT: I've added an image to illustrate what I mean by an alternate sorter.
