Just a cool fact I want to share:
You can actually boot LAKKA on the retrostone, although it's unusable because you can't read a word on the screen of the retrostone and the controls don't work also. You can connect a keyboard though and change the scale of the UI, but still...
Download LAKKA for the orange pi pc. Burn it to a µSD card.
You have to change extlinux.conf on the µSD before booting, to something like this:
LABEL Lakka
LINUX /KERNEL
FDT /sun8i-h3-orangepi-pc.dtb
FDTOVERLAYS /overlays/sun8i-h3-tve.dtbo
APPEND boot=UUID=1601-2453 disk=UUID=d0e2b1d4-1814-45b2-981c-4285f8c43864 quiet console=ttyS0,115200 console=tty1 video=Composite-1:720x480@60 vmalloc=320M
I marked in red what should be added/changed to. Strange thing is, you have to set video to 720x480. If you set it to 320x240, it doesn't work.
When you boot the Retrostone 1 from the µSD card you will see the LAKKA logo pop up and after some patience, the UI will come up.
The cool thing is, LAKKA is running mainline kernel, so this means mainline kernel works now on the Retrostone 1.
By the way, it also works with LibreElec.