Not necessarily a high priority, but the layout preview could benefit from some visual fixes (love the functionality though).
NITs
the corner radius for each app is just massive relative to the radius of the containing screen (which I actually think has no corner radius)
taskbar is not to scale (I also think it should just be a line straight across along the top edge of the taskbar, rather than a long rectangle with a boarder on all sides and rounded corners) for what it's worth, the taskbar looks more like an extra long window rather than the taskbar, and i really only confirm its the taskbar when i hover a minimized app
when i hover over apps whose edges align with the edge of the screen, the boarder gets cut off (you can see it in the taskbar above, and here's another example below)
Also think this preview window could benefit from a little bit of top padding. There's a nice padding distance along the bottom, but none on the top:
App icons look a little pixelated. I personally wouldn't mind them being a little smaller (maybe the same size as they are in the list view) if it means they don't look pixelated. (Also doesn't look like we pull the same icon that those apps use in the taskbar - see Settings app or Spotify).
the default width of the editor window feels a bit overkill (too long), it makes the preview window have these huge empty space margins on the sides, and for the list view of apps, the middles of each rows are just dead space with no content
Not necessarily a high priority, but the layout preview could benefit from some visual fixes (love the functionality though).
NITs