An interesting idea that's definitely worth exploring. However, I think the conflict between tree-based editing and normal editors is completely unnecessary. In fact, you can actually get basic tree-based editing today in Emacs! The easiest language to support like this is Lisp because its syntax is about as close to pure tree as possible. And, indeed, Emacs has had structural editing for lisp for a while in the form…
It's pretty powerful, and I use SHM in my Haskell stuff to mostly good effect. I just have some issues involving the default indentation that I need to get round to fixing, and I haven't figured out how to surround a block with square brackets yet. But otherwise, very good stuff.