A Rust implementation of Android's Binder

> the other advantage is the service activation—though that got kind of superseded by systemd though a similar mechanism

Several D-Bus implementations now use systemd as an optional or required backend for service activation in preference to doing the fork-and-exec themselves, but it's still the message bus (the broker) that needs to be responsible for the autostarting behaviour where it recognises a message addressed to a not-yet-started service, asks for the service to be started, delays delivery of the message until that has happened, and avoids sending an error reply "service is not running" in the meantime.

systemd would not be able to do this without the message bus's help, because it's the message bus that needs to implement the delayed re-delivery: it wouldn't work without being integrated into the more general logic for how and when to deliver messages.