I'm not aware of another repo. The best I can suggest is having a look at my old LE 7.0 branch for AppleTV which is here:
Comparing LibreELEC:libreelec-7.0...chewitt:appletv-7.0 · LibreELEC/LibreELEC.tv · GitHub
If you look at the core changes made to re-add i386 support to the build system, the basic process will be the same, then it's trial and error to find all the packages that are x86_64 only and re-add support for i386.
Kodi does not transcode, so no.
Create a USB using LibreELEC-Generic_x86_64-9.0.0.img.gz and then boot it with a USB keyboard connected. At the syslinux prompt hit any key and it stops boot. Instead of running the installer (the default option) use/type "run" mode and it should boot into LE from the USB. Enable SSH or use the local console on CTRL+ALT+F3 to mount the boot (first) partition on the internal drive and delete the boot files, then copy the contents of /flash over to replace and update the boot files. Reboot without the USB bits connected and it should now boot into LE. You be glad to know that LE added a check in the update process (about 2.5 years ago) that will abort the update when the image filename doesn't match LibreELEC-Generic_x86_64-<version> so it will take deliberate ignorance to repeat the mistake.
NB: OE installs often have a lot of crap still installed due to some dubious packaging decisions in the 8.x image. You might want to consider backing up the essential files and then doing a clean install and manual restore to effect a spot of spring cleaning.
Ooo.. nice work! 
RAR archive support has moved to an add-on which can be installed from the LE repo.
Team Kodi are largely responsible for packaging the game add-on(s). Team LibreELEC are responsible for ensuring something compiles and we do the actual building (hence add-ons are in our repo). The fact that something compiles doesn't necessarily guarantee things will actually work; everybody is still learning about this stuff .. and the GUI still needs a lot of refinement to better guide users on how things should be used.
Does that mean that the 3.14 Kernel for amlogic devices is going to be replaced (Vim,Odroid C2, etc.)?
Correct. We've been working on this for the last year and are now a couple of months from having things in a fairly decent state. GXBB/GXL devices are actually very usable already, GXM hardware (VIM2) needs panfrost to mature a little first (but also active WIP).
You can have a poke at current test images from balbes150 here:
1. I'm not aware of any issues with the tethered hotspot feature; the sysctl hack should not be required.
2. Use the LE settings add-on (or connmanctl from the command line) to change the DNS servers; if none are set manually, whatever your router gives via DHCP will be used instead. If you need a gateway that's different from the one provided by DHCP, set the IP details (including DNS) manually.
Currently not working but being actively investigated. No timeline on when something public might be ready.
milhouse will pick that commit into his builds for some testing and as long as no issues are observed we'll add it into an update while reminding the Pi Foundation folks that the issue is still outstanding. The patch will probably miss LE 9.0.1 (which is due imminently) but land in LE 9.0.2. Keep using the modified test image for now; it's better to have a system that works with a few more unresolved Kodi bug than something with fewer bugs that doesn't work.
Not possible until HDR support gets added to the Linux kernel. It is being actively worked on (by Intel engineers).
Ahh.. would be good to test then. Can you spin an image for the user?
Raspberry Pi 3 built-in WiFi SSH NTP Problem · Issue #1519 · raspberrypi/linux · GitHub
links to Sets the BCDC priority to constant 0 · raspberrypi/linux@983cf7a · GitHub which from the age of commits i'd expect to be included with our kernel, but it's not something I can test (am travelling at the moment).
I've pinged some of the pi folks, but traffic to that GH ticket might be a good idea too
File locations discussed on the Kodi wiki map to:
/storage/.kodi/userdata/server.key
/storage/.kodi/userdata/server.pem
I've no idea if anything else is needed.. but we haven't done anything to disable the feature.
Currently VIM1 only. VIM2 support will come with the switch to modern kernels (soon, but not this week).
As I said before, I have no knowledge on how the Windows stuff works.
Looks like the device-tree was merged for Linux 5.1 (see [v5,1/5] arm64: dts: rockchip: Add DT for NanoPC-T4 - Patchwork) so it should be picked up in the mainline rebase work at some point. If someone submits a valid Linux 4.4 device-tree to @kwiboo's rockchip kernel repo it can probably find it's way into the ongoing alpha releases for RK hardware. Otherwise I have nothing to add .. I'm not that involved in the RK work.
