Systemd is ready to begin immediately making use of IDMAPPED mounts as part of

Is ready to begin immediately ..... give us a break you parasite of systemd-parrot ... systemd and its mothership has created this to extent its control and influence from kernel to gui.

Why don't they jump a few editions of phoronics and say "Linux, a systemd feature" ...

Guys, this is not specify to systemd, this is specific for containers (A.K.A namespace) environment
https://lwn.net/Articles/842423/
For sure systemd will jump on it before i have the time to finish my sentence but this feature was asked from a long time now by container dev.

I may not know at all what I am saying, but it seems to be after dbus-logind/(systemd) everywhere, everything communicating with everything, container solutions have become harder and harder, than it is without dbus-logind. So it appears as a problem was created so a specific solution can be justified. I think I've seen this a few times before.

It is like you place a snitch in every corner of the city and have a centralized "intelligence" collection, of who is doing what where and when with who, and then you make the necessity to isolate people from other people, but in a way that you may be isolated from others but the snitch always knows.

Enjoy your privacy, now user one doesn't see what user two does, but big brother is watching both.