dbus-daemon-launch-helper is needed only for “D-BUS System Activation”, a feature similar to systemd activation where dbus actually starts daemons itself rather than having them started through the init system with the proper initial privileges, which obviously require a setuid helper. This is described in:

http://dbus.freedesktop.org/doc/system-activation.txt

Such a setup is almost certainly an undesirable risk in a hardened environment, and it’s not clear that it’s needed or useful at all with proper use of OpenRC. Thus, dbus-daemon-launch-helper should not be installed setuid by default. Moving it to a separate package (e.g. dbus-system-activation) may be an appropriate solution.

(from redmine: issue id 3313, created on 2014-08-27)