Sometimes they can, sometimes they can't, this has been addressed elsewhere in the thread so you should not be bringing it up here.
I have read (and posted) this thread extensively, and There are no truthful examples of a portion of Systemd that cant be replaced except udev which has to be an integral part of the init system.
There are several examples in this thread, and there have been several examples in prior threads, and there are several examples in various blog entries which you could find with google if you knew how to internet, bro.
Every time I ask for examples, I get a response just like yours: "Look around, examples are everywhere!". They are not. Even in this thread, there are no examples whatsoever. The closest I have seen to examples are either lies, or half truths, like the statement I found indicating that Systemd replaces ntpd (it does not, but it does offer an alternative to ntpd, which is not required). I have only been able to conclude that people are opposed to Systemd for personal reasons which I can only guess at the reasons for. Those reasons seem to have no technical foundation, but mostly appear to stem from a long working understanding of xyz init system, and a healthy fear of the new and unknown.
My personal suspicion is that there are a lot of Sysadmins out there who have been working with sysvinit like systems for a very long time, and are comfortable with the various scripting languages involved, but with Systemd being written in C, it scares them to think they would have to understand C in order to debug their boot-up problems in the future. I can fully understand this particular bit of paranoia, but it is simply paranoia, nothing else.
No, balls is taking away someone's lunch and replacing it with a shit sandwich,
TANSTAAFL. Linux doesn't belong to you. You haven't paid for it, you didn't build it, so don't whine when it isn't what you want. Furthermore, no one is taking anything away from you. You are still free to continue using whatever distro you use today. It is yours as long as you like, but no one owes you free updates, in fact no one owes you a damn thing, so get over your self righteousness, because you haven't the right.