Linux

Clearly post does not understand kernel booting. Initrd will never go away, you need a way to tell the kernel to start systemd, which is usually part of initramfs. Both can be compiled as part of the kernel image which can be directly booted from EFI. So basically EFI->Kernel->Decompress InitramFS->Run Initrd Boot Script (usually ends by kicking off SystemD). Initramfs is compressed to reduce boot partition usage, load faster into ram (more noticeable on HDD). You want the bare minimum of kernel modules available in initramfs to load storage drivers, filesystem, LVM, LUKS. Everything else should be modules on the root filesystem, unless it needed for boot. You can compile these static into the kernel too. Generally modules are preferable as they can be unloaded/reloaded if there is an issue. Also updating initramfs modules is annoying. I wrote my own initrd scripts and custom initramfs. You can build it all with bash scripts and configure the kernel to include the payload.