The answers are there, you just don't want to admit they are right answers...

It's not a safe assumption unfortunately. There are distressingly many machines out there which deliberately are run without batteries (lower field maintenance) and which hence have the time set at boot. Note that "ntpdate -s" implies setting the time - not slowly adjusting it. Even if you discount this example, I have a strong sense that there are many other high-level events (e.g. the network and printer examples).

What exactly is the "native notification logic"? (Note that many events are application layer).

Also, I'm not saying systemd needs eventing logic. I'm asking whether it makes sense to try solve these problems in a init process, external to applications. (for value of apps that includes those that would be started by it).

In short I'm asking whether actually its user-space that needs fixing to cope with differences in and changes to environmental state? Because it seems that doing that correctly would allow a not-too-fancy init to fire off apps in parallel and not worry about dependencies, as you argue systemd should be able to do with good apps. It seems applications will have to be modified to do this anyway, to get best effect from systemd.