Most of the functionality is present but many important bits are still being developed.

  • I don’t think this is as much of a problem, proprietary hardware is a thing on x86 too. The two big problems are a lack of boot standardization, and vendors not upstreaming their device drivers. A lack of standardization means it is difficult or impossible to use a single image to boot across different devices, and the lack of upstream drivers means even if you solved the boot process, you won’t be able to interface with peripherals without using a very custom kernel.