Thanks, great platform change!
It breaks backwards compatibility. For example a user may suggest a completely new and different way for the Families feature to work. Even if it's a brilliant idea, it would likely break thousands of existing projects that already rely on the feature working the way it already does. Users whose projects break between Construct versions rightly get upset, so we strive to ensure compatibility between Construct updates. Ideas which would obviously break this are not something we can really do in practice. We can in some cases add a parallel feature and try to phase out the old one, but this is technically complicated, and confusing to users who wonder why there are two options and which one they're meant to use.
If in this example, Families cannot be changed or updated, but the new feature suggestion would be a big improvement: the parallel feature sounds like a good idea, and perhaps one way to offset the confusion for users would be to name it so that it's clearly an upgraded version. Like maybe something like "Families 2" could appear in existing projects? That way people can opt into the new families, without breaking their old projects. And in fresh new projects maybe you wouldn't even need to show the old "Families v1"? It's a bit weird, but maybe it's still better than never being able to update some old features.