Upstart and readiness
Note that the readiness problem means that Upstart currently doesn't really work as intended for many server daemons. It's a known problem that has gone unadressed for a long time.
Regarding Debian: following the discussion on debian-devel, no decision has been made regarding what's installed as default, but systemd is supported and it seems to me that it just has the most momentum, both inside and outside Debian. Extrapolating that I think the most likely outcome is that systemd one day ends up being the standard, with a wrapper to generate init scripts for Hurd and FreeBSD kernels, unless someone steps up and implements systemd on those systems.
Regarding launchd: the systemd developer addressed that and you can also find some comparisons online with Google. It just doesn't address a lot of the issues that systemd addresses, and it's probably unlikely Apple would like to take a lot of patches addressing problems that are specific to Linux distributions.