The only thing in your post I really want in Linux is a better bootloader the FreeBSD one is pretty neat, I've seen bootloaders that include kexec to change Linux kernels in early boot. But I seldom see the need for a better pre boot env, and I think this is the general consensus. Also the key to boot speed is to forgo initramfs completely, at least if you look at those sub 500ms boots that are out there.
Seems there is a ever-growing list of Linux bootloaders. Which ones are not satisfactory and why.
I was very satisfied with the BSD bootloaders. Plus the kernels comply with the multiboot specification so it was possible to use other bootloaders. This way I could boot kernels from different BSD projects from the same USB stick using a single bootloader. I do not use GRUB.
Though that seems for older hardware, mostly. The one for current systems is in development. Anyways, on older hardware it enabled otherwise impossible things for me.
