[k2eric]

Hi and sorry for the delayed response. Thanks for your interest and great questions. I'll do my best to reply but invite any other voices to chime in.
 

Would using Kodi in a container limit the exposure/damage that a rogue kodi addon could do, like deleting media or wiping system folders etc? and/or simplify upgrades?

Using Docker arguably reduces the attack surface as most of the host system's files, processes, and devices are hidden from Kodi and its add-ons. I give the Kodi container read-only access to my media library, full write access to just the Kodi home directory, and drop all Linux capabilities. So IMHO, yeah it's safer than an out-of-the box Kod install. To be fair, it also takes more setup than a typical Kodi on Linux installation.
 

Also, will controller input (e.g. bluetooth xbox controller, working perfectly with the ubuntu host) & kodi-retroplayer cores work inside the container?

Can't think of a reason that either bluetooth or retroplayer wouldn't work. It might take some extra packages in the container (i.e. a custom Dockerfile) and/or providing the container with access to something from the host's /dev. I'm happy to discuss this further.
 

Trying to understand the motivation to dockerize kodi, I am new to docker overall but keep hearing about it. On the other hand, I am increasingly using flatpaks for apps in my linux desktop (and also discovering flatpak's limitations, such as no OpenCL for apps etc)

Personally, I run a bunch of services (file sharing, backups, etc) on my HTPC, and my goal is to run as much as I can in Docker containers as each app can have its own dependencies, is easy to upgrade, and is isolated from everything else running on the system. Based on my limited knowledge of flatpak, and similar techologies like snap and appimage, it seems that Docker is a little more low-level. Docker also has a massive user base (see AWS ECS and Kubernetes) and will be around for the long term.