You can see my github commit log which is linked in the OP. I currently use 4.14 kernel, Mesa 17.3-rc4, libdrm 2.4.85, libva 2.0.0, intel-vaapi-driver 2.0.0 and xf86-video-intel from git. I don't have coffee lake, but it'll definitely work better than the already outdated stack in LE 8.2. Give it a shot.
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OK, I would like to give it a shot.
I first have to install latest stable LibreELEC (Krypton) 8.2.0 and then update to your version, don't I?
My problem is, that I can't even launch the latest libreelec because it's still on kernel 4.11.8 which does not support coffee lake's GPU, meaning I get into kind of a boot loop telling me X cannot start. So I find it hard to update...