Thanks for the nice words (and the other commenters too)! I had been using it for some time but I am happy that I released it since people seem to like it.
I think it’s fine to keep this a separate repo, I’ll put a pointer to it in the kakoune-mysticaltutor README. It looks good, thanks for your work!
PS. All your powerline.kak links actually go to plug.kak in the README.
PPS. I saw in your screenshot that the session name in status-left in the tmux statusline is brightred instead of red, since WT doesn’t support bold and tmux doesn’t seem to disambiguate bold and bright as WT understands it right now. You might want to change it to remove the bold, i.e.
set-option -g status-left '#[fg=red] @#{session_name} '