Features:
+* maybe introduce container-shell@.service or so, to match
+ container-getty.service but skips authentication, so you get a shell prompt
+ directly. Usecase: wsl-like stuff (they have something pretty much like
+ that). Question: how to pick user for this. Instance parameter? somehow from
+ credential (would probably require some binary that converts credential to
+ User= parameter?
+
* sd-varlink should probably enforce a limit on queued outgoing replies
* systemd-firstboot: optionally install an ssh key for root for offline use.