The problem isn't support for the ARM architecture in general, it's the support for this particular board.
Other boards like the Raspberry Pi and many boards based on Rockchip SoCs have most of the necessary support mainlined, so the experience is quite painless. Many are starting to get support for UEFI as well.
I'm not a compiler expert... But it seems each ARM64 board needs its own custom kernel support, but once that is done, it can support anything compiled to ARM64 as a general target? Or will we still need to have separate builds for RPi, for this board, etc?