Yes, Libreboot has UEFI now!
Still probably won't boot Windows.
My motivation here is U-Boot also has a slew of other boot methods, and will make dealing with Linux distros a lot easier for most people; it will also be of great help to BSD users, who currently rely on SeaBIOS in Libreboot.
I will provide a "SeaU-Boot" setup in the upcoming release, where SeaBIOS has a bootorder file loading U-Boot first, while still allowing other options via ESC menu. Same concept as SeaGRUB but with U-Boot.