It could be an option for the selector combinator. For a simple option, not overpowered and more in line with the idea of a basic building block:

Using the layout of the "Select input" option:
1) New option: Select freshness
2) Replace the index with the signal to monitor
3) Replace sorting with ...

The sole purpose of this pipeline is to extract holmium ore from scrap and trash everything else. It's built with legendary entities (except belts, circuits) and works with scrap research up to level 30. It should work fine with lower research levels, however the ore output will be lower.

It can be ...