My suggestion would be to modify the Emacs major modes, not to
introduce special stand-alone modes. Making the changes directly in
the existing modes is a faster way towards tree-sitter integration.
Sure! If I write a patch for js-mode today, will you be able to apply it to the feature branch? That will be the simplest thing to do, seeing how I've already made typescript support, and supporting all the cc mode styles etc is a bigger effort. I'll just put it behind a "js-mode-use-treesit-p" defcustom or something like that?