No more boot loader: Please use the kernel instead

Yeah, nah. This only throws more complexity under the rug.

Among other stuff, whatever is booting your computer needs to 1) find the kernels that you have, 2) find any other OS that you might have, and 3) allow the user to pick one of those. You can either use a specific tool for that (bootloader) or dump those roles into the kernel, but you can't get rid of them without breaking a lot of stuff.

what about secure boot?

Regardless of the above, the owner of a device should be able to turn secure boot off; devices not allowing so are broken by design, to prevent your full ownership over it.

GRUB2 is really complicated.

Part of the complexity is intrinsic, as explained. And if you're concerned about the additional complexity from the implementation, the solution is a different bootloader, not ditching the concept altogether.

I stopped watching the video at 8:22, as she was talking about bugs.

The simpler solution is to simply pour more development into GRUB2, not to throw the problem into the kernel devs' hands, as if it was some sort of hot potato.

The "looks for other operating systems" is huge for any desktop use with dualboot, recovery media, and plenty of systems have utilities like Memtest86 through the boot menu.

Grub always seemed weirdly complex yet incomplete- the idea that you had to pre-enumerate every bootable OS made it worse than rEFInd to me.