Every client operating system under the sun implements a DNS cache, its part of the intended design of DNS. This is just systemd's bikeshed of a function alread

Every client operating system under the sun implements a DNS cache, its part of the intended design of DNS. This is just systemd's bikeshed of a function already available on Linux, via nscd. Without caching, all DNS queries degrade to worst case behaviour, which is a recursive query involving 4-6 or more round trips, starting at the DNS roots (which, good luck finding them, since you don't have their addresses cached, which is exactly what the root hints file is). As for invalidating the cache when network configuration changes arise, that sounds like a bug report for wherever you experienced it. Certainly I've never seen this kind of problem on OS X, nor any time in the past 10 years on Windows.