Theming Grub is definitely not a Fedora priority.
It comes with the opportunity to boot different kernel versions and to ensure rescuing the system when there is an issue.
Even if it appears pitch black it does the job!
We are on Beta with F41 and will solve primarily first cases to release it to stable.
@gosling203 if you want to do some technical chitchat about grub2 and how to beautify please use the The Water Cooler section.