Since this project ended, we've have had quite a lot nice development in this front. Biggest highlight maybe is Combobulate for emacs, providing treesitter powered editing. Neovim also has treesitter and some plugins[2] to work with it. My editor of choice, Helix, also has treesitter based commands built-in[3]. All of these afaik have been released after sapling

While it now seems like this mode of using TS/structured editing to extend traditional editors will be the dominant way, I think it still might be useful to keep thinking what an editor that embraces structured editing could look like.

[1] https://github.com/mickeynp/combobulate

[2] https://github.com/nvim-treesitter/nvim-treesitter/wiki/Extr...

[3] https://docs.helix-editor.com/usage.html#navigating-using-tr...