Hm, Dracut looks like a userspace framework for building initramfs. I was wondering more about what's going on at the kernel level to switch the root. What depends on / ? Do any processes survive whose CWD is in the initramfs? Later in the article it's pointed out that systemd(from initramfs) passes the torch to systemd(in final root) while preserving state, so are any processes/ressources from the initramfs leftover or is everything cleared?

A process spawned from initramfs can certainly live on but you wouldn't want to do that because that would prevent initramfs from being unmounted. By switching to the new root you can run real binaries. You can also not switch the root and also run real binaries from the new mount but that's not very convenient is it?

Pivoting root is not the complicated. The complicated is the process of detecting and setting up the real root filesystem which can involve loading kernel modules to dhcp negotiation to http requests and more. Dracut handles all these.