Are you talking about Xi as a frontend for kakoune? If it's the UI part that you're interested in, there is also kakoune-qml[1] made by one of the regular uses.
I think creating a Xi frontend that mimicked Kakoune's modal keybindings and highlighting would be an interesting exercise, and probably stretch the set of supported ideas in Xi in a good way.
[1] https://github.com/doppioandante/kakoune-qml