As you know volumio has a pretty solid web app that you can save on your home screen.
The only thing I dislike about web apps is that they reload every time you open them. They don‘t work in the background.
I solved this by embedding the volumio ui inside a web view inside a native iOS app.
It works seamlessly. The interface is much more responsive than the standard web app.
If enough people are interested I will make a tutorial. You can do this in 30 minutes.