Given that they seem to have given up on kdbus, and is instead developing something called bus1 that appears they are not even planning to submit for inclusion, i find myself thinking that the systemd devs are these days working on enveloping the kernel.

Meaning that you no longer use kernel syscalls, but instead program with systemd in mind and then systemd talks to the kernel as it sees fit.

Just observe their actions regarding session tracking, where they are basically ignoring all data from the kernel about sessions.