Debian testing/unstable deserves more user and developer influx from Ubuntu castaways.
Googles change to debian-testing reflects my own rite of distribution passage. I used manual /etc/apt/sources.list upgrades within Ubuntu so often, after Unity was abandoned, there was no reason to stay on Canonicals flavour.
After a year on testing I went to unstable and subscribe to bugs affecting me from time to time. Usually there's either quickly a workaround or a flatpak as last resort. Not something I'd install on the family pc, but testing or unstable is a good choice for developers.
Contributing to Debian and adjacent projects like GNOME and freedesktop.org got easier (or standardized?) since they all run a gitlab instance each.