@Konfekt Unfortunately I have to to say that I don't plan to do that, because I don't have much time on vim-ctrlspace now (and actually I use popc now).
This PR was done at my start time with using git-pr and learning vim. So the commits aren't so beautiful and reasonable. Regret for this.
If you want to provide what this PR does for vim-ctrlspace, I think it's better to rewrite this PR with new features of neovim/vim like floating window, popup and json.
Finally, thanks vim-ctrlspace and all its contributors. :)