The wider concern here seems to be that Debian's choice to inch its way toward systemd being the defacto standard, could imply that all of systemd's choices will become Debian's choices. The focus of this list seems to be to get out in front of issues before there's not enough time to react.

A more narrow form of my question still stands: Does an off-ramp need to be provided so that upstream package maintainers may continue to provide sysvinit enabled packages should the current distribution actively forbid it? It would be worth thinking about the response times required to meet a need like that.