The Debian init system general resolution returns

Look, mount table is trivial to build from scratch - open /proc/self/mountinfo and read it; check the code in systemd that does this work. Moreover, keeping it updated is also easy - check the same code.
It's not really worth bothering with any IPC, let alone the one of push instead of pull variety.

And if you do insist on IPC, for some reason, you could bloody well start a caching daemon on demand (with e.g. timeout for inactivity). There's no reason whatsoever to keep that in PID 1 or anywhere near it.

We already have mechanisms for parallelizing. Had them for more than four decades. Called "processes"...

Having systemd forwarding a bunch of stuff it gleans from the kernel is asking for bottlenecks, for no good reason. System calls are not going away; not unless you want a truly monumental bottleneck with systemd playing the role of Mach server. Even then read(2) and open(2) wouldn't disappear, including those of /proc/self/mountinfo...