There are a number of filters (ancestral, descendant, relationship) that would be much more useful for purposes of working with DNA matches, and perhaps other purposes as well (tracing things like prevalance of heritable conditions), if those filters could optionally limit their scope to biological relatives.
From the user perspective, it would be very simple: just a checkbox. But I imagine it would impact many places deep in the code. When selecting parents (or children) of a person, it would need to check for the “birth” relationship (child reference type?). When selecting siblings of a person, it would need to make sure they had at least one birth parent in common. So that sounds like potentially a lot of work in a lot of places.
Is there another way to approach the problem? I think I could get by with creating my own multi-part (stacked) custom filters if just the existing “Parents | Children | Siblings of <filter> match” filters had such an option, or if there were some new basic filters to work with, such as “Biological parents | children | siblings of <filter> match”.