Would anyone use this for real programming, if it supported your favorite programming language? I know "supported" is a loaded word there, but just take that to mean: supports all the basic edits you need, in composition, to make any complex edit, but not fancy refactors or fancy language-specific stuff.
Features like the mentioned tree selection do make sense. But I prefer tools to be more like a library than a rigid framework. Give me the ability to perform powerful transformations, but don’t put me in a straightjacket that disallows non-well-formed intermediate states.
This Pantograph somewhat reminds me of that lightweight structure editor, though Lapis is able to find regularities on the fly without a need to follow a perfect tree structure, just by finding bottom-up syntax of language elements (mostly HTML and basic data types).
https://en.wikipedia.org/wiki/Lapis_(text_editor) (Look at the links for an archived download page)