I really like this, I've always thought that git needed to support diff modes different from textline-based because even if this is fit for most programming languages what you really what is to see differences between ASTs (take into account those absurd change counts when just changing the indentation or imagine a normal diff of LISP source).
Maybe there's some way of replacing git with noms to get there(even if it may be killing flies with cannonballs)
For what it is worth, in my experiments most ASTs (the rare exception being something like Roslyn's C#/VB ASTs) don't do well in "degenerate states" such as a partially finished files. (A good source control system should let you commit unfinished work.) I did have great success using a syntax highlighting tokenizers. I was able to create really nice-looking character-based diffs that were relatively semantic, quite quickly. I've not tried to use that as the basis diffs for something like git, though I've suggested trying it before.
