@lanodan
>Lack of library management so you can end up with pacman libraries being missing?

That shouldn't normally happen. The library pacman uses to do most of the work (libalpm) is owned by the pacman package. I've seen AUR helpers break when used as "system updaters", because they aren't rebuilt against the new version of the library and the linker properly throws it's hands up when the helper tries to launch itself again and can't find the proper version shared library.
I've never seen it fail this spectacularly and the only cause I can think of is that it only partially extracted the new pacman package or one of the dependencies (lack of free space, power outage, killed by user/system).

Btw sending ctrl-c when pacman is running any kind of package transaction (include pre/post hooks) is the fastest way to innocently kill an Arch system. The internal package database isn't updated properly, which will lead to pacman confusing package versions and your initcpio very likely missing.

>Package manager fails to update the signing keys? Urgh, this shouldn't happen.

I've seen this happen only when it couldn't verify the signature of the new keyring package based on the old keys it had. Which is a common problem if the system is left sitting for a month or two without updates. And probably the reason why pacman doesn't enforce signatures for local package installs.