Mixing zones I'm sure are fine in some areas, but a lot of potential cyclists (like the very old and very young) are going to be intimidated by being with cars,

Mixing zones I'm sure are fine in some areas, but a lot of potential cyclists (like the very old and very young) are going to be intimidated by being with cars, period. Unless you heavily road diet the place with speed humps and other traffic calming measures, to the point where it's super obnoxious to drive in, at which point what is the point of still having cars there? The Netherlands is probably Example #1, and IIRC they commonly have mixing zones for streets right in the city center that are rather pedestrianized, outside of that you'll mostly see separates bike lanes/paths.