The most recent discussion prompted me to submit an issue for Goneovim about using Cmd+/Cmd- for font size changes. @akiyosi very helpfully wrote a lua script that would do that. I would have had no idea about how to implement this functionality.
(Not surprisingly, the keymap strings need to be different for different operating systems or keyboards. For example, on my Mac laptop, Cmd-+ is really Cmd-=, i.e. <D-=>.)