OK, so I have compiled a set of extra libs that are required for 1.7.4 to run on LibreElec 8.90.005 (though only for Gen, since I don't currently have my Pi running).
1.7.4 requires 109 MB of libs to run. It works! - but there are some black squares on some menus where icons are supposed to be. I am not sure why this is; I just copied the binary and all the 85 required libs, so maybe I am missing something. (Edit: I have the original deb archives in tar format, there is an asset directory which is supposed to be in /usr/share/libretro)
You can get it here: retroarch-gen.zip
BTW, I was right. LibreElec is compatible with Ubuntu 16.04.
Thanks but I already have both RPi and Gen RA 1.7.4 binaries compiled, I use Lakka project to compile using LE toolchain so it needs no additional libs, just the ones missing in LE9, lakka is still based in LE8.
When I can get some free minutes I will upload the updated pre-release to test