App layout library

What do you all think about something like this: https://www.espruino.com/ide/?emulator&upload&gist=8cad25a87c633e2c614d0eefa52fcd2e

The layout for an app might look something like this:

var layout = { type: "v", content: [
    {type:"txt", font:"6x8", label:"Temperature", col:"#f00", halign:0, pad:4},
    {type:"h", content: [
      {type:"img", src: ()=>atob("CgoCLguH9f2/7+v6/79f56CtAAAD9fw/n8Hx9A=="), valign:0, pad:4},
      {type:"txt", font:"30%", label:"20.0"},
      {type:"txt", font:"6x8", label:"'C", valign:-1}
    ]},
    {type:"txt", font:"4x6", label:"left", halign:-1},
    {type:"txt", font:"4x6", label:"center"/*, halign:0*/},
    {type:"txt", font:"4x6", label:"right", halign:1},
    {type:"custom", _w:64, _h:64, render:myRenderer, fill:true},
    {type:"btn", label:"More...", click:() => print("Hello")},
    {type:"custom", _w:64, _h:64, render:myRenderer, fill:true}
  ]
};

So you can have horizontal/vertical alignment, the ability to fill available space, padding and color. By putting in elements with fill:true you can pad out certain areas too,

Nothing sorted for button handling yet, but so far the code seems like it'd be reasonably fast and compact.

Maybe the thing to do is to look at existing apps and see how easily they can be converted to use it.