DBus is a system-wide messaging system. It's for stuff like notifications and system-wide events, ...or so do I think. But the aim is to allow all programs, running system-wide, to announce anything for others programs to react to.
This post requests people to use Varlink instead.
This is similar to the PulseAudio versus Pipewire and X11 versus Wayland situations.
So, Poettering wants to make life difficult for everyone using something other than his precious again by transitioning from the normal standard for IPC to something hardly anyone has ever heard of or uses that's based on JSON? Seriously? 🤢
It's not just "hardly anyone," it's "literally no one." Varlink was invented by the systemd developers out of whole cloth specifically for this purpose.
This has always been the whole point behind the Trojan Horse that is systemd. Now that Poettering/Red Hat control the entire userspace across virtually all distros, he/they can use it as a vehicle to force all of them to adopt whatever bullshit
he thinks of next.
This is what the Linux ecosystem gave away when they tossed their simple init system to adopt the admittedly convenient solution that is systemd. But in reality, the best solution was always to drop init, and instead replace it with an alternative that was still simple to replace if the need should arise. But now that everyone is stuck on systemd, they're all at the mercy of Poettering's Next Stupid Idea.
Convenience comes at a price. systemd is the Google Chrome of Linux userspace. Get out while you can.