I wonder if this will impact Debian's current debate [1] on init systems. A minimal systemd-compatible init system seems like a real contender here, and this project shows that there're both interest and capability for developing one.
It's also only two months old. So I would say this a toy project. Of course, that it is a toy project right now does not preclude it becoming a real, robust init system in the future (just look at where the Linux kernel started, after all) but I do not think it is currently relevant to the Debian debate.
https://buildd.debian.org/status/package.php?p=rustc
Looks like there is a bootstrap issue, rustc build-depends on cargo, which build-depends on itself.