This is mostly written so that I remember how I installed it the next time I reformat my entertainment box to try something shiny and new. But as it might interest someone, I put it out there.
Thaks to ProfessorKaos64 and his SteamOS-Tools, it is relatively painless to install kodi on SteamOS and access it through Steam's big picture interface. I could have left it at that, but two things profoundly disturbed me on SteamOS. First, try as I might, I could not find any easy way to boot into Kodi directly and still have a working steam controller. It might not seem like much but I use kodi almost every day and Steam maybe twice a month. Secondly, SteamOS was extremely unstable on my machine which defeats the entire purpose of having a fun time. (RAGE is not fun time.)
So being a long time ArchLinux user I did a minimal install of Arch with only Kodi, Steam and OpenBox installed (as well as samba, gdm and a few other things.) I set up GDM (I had a small issue with LightDM)to login automatically into my gaming user with an openbox session. Once in my
~/.config/openbox/autostartcontains the following lines.
kodi & /usr/bin/steam -silent %U &
This boots into kodi with steam in the backgrounf (In order to have the steam controller working.) To switch to steam, I installed this wonderfull plugin SteamLauncher plugin. And I can now continue to entertain the Idea that I will play Civilization 5 if I ever have the time.
Next step, set up lib retro.