Since BootLoderSpec by default the GRUB entries are specified in a bls.cfg file provided by the kernel RPM, which in turn it is used to generate the corresponding file in /boot/loader/entries. There, the grub_class is set to kernel, so GRUB themes will not display an icon for Fedora unless manual adjustments are made.
I know Fedora is not very keen on bootloader theming (after all the good old console output ensures the maximum compatibility across a wide range of systems) but my understanding is that the grub_class has this sole purpose and Fedora could provide a sensible default.
My question would be: where could be the right place to bring up this proposal?