Systemd is actually a great tool for building your own desktop. It's user services/units are perfect for long running user process. I use it extensively for my Openbox setup. Running compton, conky, redshift, xbindkeys, urxvtd daemon, setting the wallpaper, running the screenlock program, and my calendar reminder all as systemd services.

The only thing really changing right now is Wayland and the switch from window manager to compositors and the related support software. There are getting to be a decent amount of options in that regard with a good crop of lightweight compositors and tools starting to mature.