probably not a huge deal, but bigger implications

I suspect what will happen is like with elogind, someone will provide a systemd-free version of the interfaces that Gnome needs out of systemd. I don't think it's tight coupling as much as it's one of the few interfaces to do what they want without having to reimplement a worse service manager themselves. Support for another service manager could be added, or an adapter for that API.

I think the bigger insight is: the system layer is pretty important (see Benno Rice's talk); perhaps there should be an effort to make that kind of functionality available across OSes, and have an API for it. The POSIX of service management, if you will.