Thanks for updating the systemd-boot article with the new USE flag for systemd.
As contributors we need to be careful, however, that we aren't removing important documentation when we make changes - In this case the
boot USE flag is only available for 'testing' versions of systemd; everything marked as 'stable' in portage still requires the
gnuefi USE flag to enable systemd-boot/bootctl functionality.
It's fine (and encouraged!) to drop superfluous or obsolete instructions, however if things are in a state of change please consider documenting _both_ options so that, when a method ages out, older instructions can be removed at the appropriate time.