Programming by modifying ASTs sounds very interesting and I really like Lamdu examples. I see, however, many problems, as not being able to introduce even slightest modification to the code using terminal, not being able to use textual tools, and problems with source control interop.

The last one is probably the most serious, as it doesn't seem to be enough to plug new diff tool into git. There are still places like GitHub, which are hard to modify. That would mean one would need whole new ecosystem for such language.

Having underlying textual format, possibly based on s-expressions might help. You could modify it using AST editor, but still be able to read the code as text and diff it. Other option is to have two-columns editor, with one column being text source and the other AST, making it possible to edit any of two and have the other updated.