Thanks for the suggestion, but I've already tried Yatse, Kore and all the other Kodi remote apps. They work OKish for music, but are next to hopeless for web-radio, audiobooks and podcasts. It was the frustration with these clumsy make-do options that lead me to try Volumio + touchscreen. Which works like a normal hi-fi or radio. No need to switch on a TV or hunt for a smartphone. Just tap the touchscreen and away you go.
Once you try Volumio you realise just how much audio on Kodi is compromised by a structure designed primarily for video content. Don't get me wrong, LibreElec is fantastic for video. I use it everyday for films, shows and live TV. It's just not a great solution for a home hi-fi in a kitchen or bedroom or wherever.
I just wondered if it'd be possible to make something like Volumio but with a lighter and more robust chassis, and with more chance of mainstream acceptance and 3rd party development.