I tried to search for a solution to this but only found things 2+ years old so I'm not sure if any of it is still relevant. Anyway, I migrated to Shield from a dedicated HTPC that used Kodi as a frontend. I love my Shield, and love Kodi, but it really is more of a frontend or launcher than an app itself. So is it possible to make it so the home button on my remote goes to Kodi rather than leanback? if it helps at all, I use a Harmony remote, so it doesn't even necessarily have to be the 'home' button, if it's possible to map another key to launch kodi, I could work with that using my Harmony and simply replace the 'home' button altogether.
Simply go to Settings/Apps and clear the data and cache of the Android TV Home app.
Click the home button, and choose your knew home app. Boom; done.