not gonna dig around in the source to my distro for examples, but here’s the hack NixOS uses to make graphical-session.target run with WMs that aren’t Gnome or KDE. since a lot of the session management stuff I want to do relies on being able to sensibly handle both text and graphical sessions (and the NixOS hack wasn’t too reliable the last time I tried it), this was one of the factors that pushed me towards using Shepherd to manage the session process tree on my systems

Can you give me some concrete examples of such breaking changes and the problems they caused?

this is a really weird question to ask, given that the context is a hypothetical systemd fork running into breaking changes in the systemd API. maybe look up a postmortem for uselessd or any of the other dead systemd forks?

What IBM says or does after that is irrelevant, I would think.

leveraging an existing toxic community against a newer, smaller one is very much a way to retain control after a fork; again, this is pretty much a known quantity, and there are a bunch of examples of it happening in cryptocurrency projects