J - Non process managed systems are simply not going to be supported.
P - Unsupported by who? Who gets to decide what is supported and what is not?
The GUI developers. Developers are who get to decide what OS components are going to be dependencies for their software. Debian changed because there were strong signs that developers were starting to introduce hard dependencies for systemd. While those could be overcome for Jessie, the feeling of the Debian people is that in 2 1/2 years there wouldn't be a choice. And while the switch in 2014/5 introduced some bugs the switch in 2017 would be much worse. The anti-systemd people (who are mainly low end system admins) refused to accept that developers don't want to deal with the ever increasing complexity managing complex process management using init. The issue was upstream from Debian, having the argument with Debian was living in denial.
As hardware gets more complex making a more complex uses possible, the underlying OS needs to become more complex to support it. There was a very disruptive change in PCs when people moved from single tasking to multi-tasking. It destroyed Amiga. It cost Microsoft something like $8b. It essentially destroyed Apple. Lots of people argued that task switching was good enough and much less disruptive. But ultimately everyone (excluding some embedded systems) switched to vastly more complex systems which had kernels with more in common mini computer kernels from a decade earlier than the CP/M, DOS and simple Unix kernels of a decade earlier. Notification is the beginning, but once notification works you are 80% of the way there to really exciting features. 10 years from now the idea of a human trying to manage service dependency will be as quant as writing assembler is today.