Which kind of ruins bootable snapshots, as your kernel isn't part of them. You could have a massive esp with ~10 unified kernels each pointing at a different snapshot, with some kind of management script to handle them, but using GRUB seems easier than that.
I think there's still value in a bootloader. You can easily load an old kernel with an old initramfs if you messed up somehow, or adjust kernel parameters.
The boot UI for most modern UEFI-Firmwares is really primitive and they usually don't come with EFI shells.