SystemD is a collection of small pieces of software. Together it makes a big system but you probably haven't paid any attention to it.
Not this argument again.
It doesn't matter how many pieces something is if the pieces are more or less inseparable. There's a reason all of those things are developed under the "systemd" banner. If you decide that you absolutely must have systemd without the crap you don't want, your only option is to configure and compile it yourself. If that's "modular" or "not monolithic", then I guess Windows is too.
If it were truly not monolithic, then I'd be able to install systemd's non-init stuff on a sysvinit system and vice-versa.
So you are saying that if it doesn't work as promised, it will suck and be broken. You just somehow know it will suck even though it's not done yet. Have you ever closed the lid on a laptop, then later opened it and found it displaying all your desktop windows and then going to the unlock screen? I hate that.... if this does work as promised, I want this.
Much, much easier solution to this problem:
1. You press suspend button
2. DE's hotkey handler catches this, tells screen locker to lock
3. Screen locker reports back that the screen is locked
4. DE then puts the computer to sleep.
Same strengths and weaknesses without ever going outside the DE except to tell the system to suspend.