I figure I'll add my two cents for as little as that's worth.
Personally, I use extlinux with a custom, barebones configuration. On my EFI systems, I
use syslinux EFI. I like the simplicity of syntax for syslinux's configuration and how
small it is, but that's me, and it's not going to be everyone's preference.
I also own several legacy BIOS based systems that cannot support EFI, and they work fine,
including my daily driver Thinkpad T410.
While I know it will still be possible for *very* advanced Linux users such as me to get
Fedora working on BIOS systems with my own bootloader of choice even if Fedora drops
support, it would create a maintenance nuisance if I need to boot a recovery ISO etc or
reinstall Fedora from scratch, e.g. in drive failure. And, of course, most Fedora users
can't easily swap out a bootloader, they just haven't spent the energy learning
those parts of the OS.
Though, that would hardly be my concern. As sad as I was to see i686 support dropped, I
could at least understand the reasoning behind it, given how few people used it and how
large of a maintenance task it was. I myself didn't really use any systems that needed
it. This, however, is different.
Personally, I despise GRUB2, that's why I switched to syslinux when distros dropped
GRUB1. I find GRUB2 very bloated, needlessly complicated, with too many magic black
boxes.
That said, dropping BIOS support simply to adopt another bootloader in its place is a
deeply disturbing proposition. There are many BIOS based systems still in service, and
there will be for quite some time.
My Thinkpad was manufactured in 2011 and still only supports BIOS. In 2012, I started
seeing EFI-based PCs on the market due to Windows 8 and MSFT's push for secure boot.
Apple was an exception, they started using EFI as soon as they switched to Intel. The rest
of the world remained on BIOS until 2012.
Are you seriously considering dropping support for all systems older than 8 years of age?
Even if I could mostly work around such a decision, it would anger me and I imagine a
great many other users, purely on ideological grounds. I would consider switching
distributions, and I've been a Fedora loyalist since 2009.
Do you remember when Linux was touted as a lightweight alternative for older PCs, and you
could install flagship distros on grandma's PC to breathe new life into it? I do. I
don't want to live in the timeline where the only distros that run on such things are
puppy linux and similar.