Mark Richter, Grub Customizer's creator, is busy incorporating the changes into the app. Some were easy and have been accomplished, some are more complex and are still being worked on.
Grub 1.99 also introduces the 'drop-in' Grub background. Here are a few threads I created about G 1.99:
Grub 1.99 Changes
Grub 1.99 Submenus
Grub 2 Drop-In Backgrounds & Font Selection