It's mentioned in the announcements.
We are making dbus-broker our default implementation of D-Bus, for improved performance, reliability and integration with systemd.
For the foreseeable future we will still support the use of dbus-daemon, the previous implementation. Pacman will ask you whether to install dbus-broker-units or dbus-daemon-units. We recommend picking the default.
For a more detailed rationale, please see our RFC 25.
https://archlinux.org/news/making-dbus-broker-our-default-d-bus-daemon/
Though it doesn't say you really need to take any action but maybe it's a start for something to look into.