Ladies and gentlemen, there's an official open source Linux 4.9 implementation. Links:
https://github.com/orangepi-xunlong/linux-orangepi/tree/orange-pi-4.9-sun50iw9
Device Tree:
https://github.com/orangepi-xunlong/linux-orangepi/tree/orange-pi-4.9-sun50iw9/arch/arm64/boot/dts/sunxi
Linux 4.9 has no mali GPU support, so I'm hoping the newest mainline or linux-sunxi would get it work.