@Sebastian I like the idea of having every line in a list of items be identical (ie even the first item allows a comma), that’s similar to how its done in rust. Make it less fiddly to reorder the items with line cut and paste operations. In rust though, the extra comma is after the last item.
My main beef with the elm-format output is four spaces for indenting rather than two. I have more vertical space than horizontal space to deal with, it’d be nice to have more indenting visible.