If we could have a feature for sorters of all types, that when the sorter is full (that is the destination belt of the sorter say a storage for potatoes is full), then the rest of the potatoes would then bypass that sorter and continue on the belt until it comes to another sorter for potatoes, if there is one. If there is no other one, potatoes (example) carry on down the line, with hopes you have a belt loop so they keep going around till it can be sorted off the belt or returned to the destination. This maybe a good option rather than letting belts get blocked or stalled due to being full. Just a tickbox for bypass if full.
Sorters and belts
The desired behavior can be obtained in the current game by adding a balancer after the sorter with a high priority output going wherever and a low priority output going back into the belt being sorted. As long as the output is at least as high quality (throughput) as the input it will only send back anything when the output is full.
I know it's not as clean as an "all-in-one" solution, but it can be done without needing a totally different setup than what you want to do.
Considering the relative costs of the sorter and balancer it would make sense to me for the sorter to also have a built-in balancer for overflow.
Agree this would be nice for there are alternate uses for something like food or even sulfur. Or even keeping machines first machine loaded fully before sending to next machine.