> The most recent Debian General Resolution on init support said something like "we chose systemd but compatibility with other inits is important"

It actually said "Systemd but we support exploring alternatives".

I read this very differently. I read this as Systemd is supported, and if package maintainers wish to include other options they may, with a view to exploring future alternatives.

I don't read this as requiring or prioritising support for previous systems that Debian has moved away from.