With respect, I am opposed to the proposal.
In essence, I think this boils down to: function > form.
I've been in too many situations where hidden GRUB menus resulted in
having to "guess" when the firmware has finally started the bootloader
and what would be a quick 5 second cmdline change turns into several
minutes of rebooting due to ESC entering the firmware configuration...
I've had similar experiences with F8 in Windows environments.
While this may be a "simple 1 time configfile change," having to enter
the menu is often an unexpected scenario so remembering to do this
*before* you run into some boot-related issue is in-itself an issue,
especially when the user has many machines/installations.
As pointed out, the plans to have a 0 second timeout in F30, requiring
some userspace preparation to enable the menu, is going to result in
issues where additional boot media is necessary if the system boots fine
but the user cannot actually log into the system.
Furthermore, the GRUB menu's "only function" is not just to allow
booting older kernels. In fact, I've personally never had to boot an
older kernel; I've only ever used the menu for cmdline edits to address
all kinds of random issues (including but not limited to graphics
issues), or to address things that weren't even "issues" (enabling
intel_iommu, for example). I often try several cmdline edits before
progress is made on a specific issue.
I think going through this effort to shave a few seconds off of the boot
time is just going to make everything harder *especially* when the shit
hits the fan... I don't think it's worth perpetuating the
Windows-ification of Fedora, either.