Well I thought it was obvious, but my reply was intended to be sarcastic. For it to be taken at face value by anyone kind of highlights the problem with the systemd approach, IMO.
The problem with your sarcasm is that it actually matches current reality. This is how various programs are busily being rearchitected to operate, or indeed already have been rearchitected to operate.
Take gnome-terminal, for example. Nowadays, a gnome-terminal-server service runs under the per-user systemd service manager, and requests to open more terminals generated by the gnome-terminal program arrive at it over the per-user Desktop Bus. gnome-terminal is a Desktop Bus client.
The gnome-terminal-server service used to be Desktop Bus activated, rather than simply run as a per-user systemd service. Ironically, given the headline on this page, this too hit a problem with a systemd release turning things on a while back. systemd version 228, in fact. All of the terminal emulator processes and the shells and login sessions that they spawned ended up sharing a single 512 maximum threads limit.
* https://news.ycombinator.com/item?id=11675129
And yes, gnome-terminal-server too suffered from the kills-screen-and-tmux problem:
* https://lists.freedesktop.org/archives/dbus/2015-January/016...
Because that brings to mind a recent project i learned about that plans to stream video via dbus...
* https://github.com/GNOME/gnome-terminal/commit/e1d641726cf0d...