This feature basically makes grub.cfg static, stops using grubby to modify the grub.cfg, and instead uses drop in script files with details about a kernel+initramfs combination, and GRUB directly finds and parses the BLS formatted drop-in file to produce a GRUB menu.
It was supposed to be default for Fedora 29, but this is being pushed to Fedora 30, mainly due to a procedural glitch that results in it not having any testing in the course of normal installation and updates of Fedora 29.
Since Silverblue uses rpm-ostree which already uses BLS drop-in scripts, and doesn’t use grubby, I’m wondering if there’s a possibility this feature can still happen for Fedora 29 Silverblue independently of the release blocking deliverables? Or if in fact all the rpm-ostree consuming projects can move to this by default?
I’ve updated the FESCo issue above, inquiring when the change can happen in Rawhide. I have no idea how the activation actually happens and if in fact rpm-ostree installations can recognize that activation.