I haven't had D-Bus problems in quite a while but actually run0 should help with some of those issues. Like, systemctl --user will actually work when used with run0, or at least systemd-run can.

Haven't used it yet so it's all theoretical, but it makes sense to me especially at work. I've used systemd-run to run processes in very precise contexts, it's worth using even if just to smush together schedtool, numactl, nice, taskset and sudo in one command and one syntax. Anything a systemd unit can do, systemd-run and run0 can do as well.

I'm definitely going to keep su around just in case because I will break it the same I've broken sudo a few times, but I might give it a shot and see if it's any good just for funsies.

Just trying to explain what it does and what it can do as accurately as possible, because out of context "systemd adds sudo clone" people immediately jump to conclusions. It might not be the best idea in the end but it's also worth exploring.