So, as far as I can tell this functionality is basically fundamental to being able to define repeated commands, i.e. this is the equivalent of concatenation in a vimscript map.
Will this become the standard way of scripting keys for vintage mode or all of sublime text? It would appear that the alternative is to extract out whatever behavior it is you want and make a whole plugin for it, which is perhaps not completely absurd but a heckuva lot more work than e.g. writing a new vim bind in the vimrc!
Even defining the new JSON definition using this plugin is much harder than in most anything else… I just really wish there was a more clean way to do it.
I really appreciate the work to make this function, though. Good job.