Out of curiosity (and I'm speaking largely out of ignorance on this), have you considered making this plugin NeoVim specific and doing it in another language you are more comfortable with?
EDIT: Also, just realize that you are the person who wrote the Practical TLA+ book...I loved it! Thanks for writing it!
Honestly the big blocker here is learning how vimscript better.
[1] https://github.com/hwayne/tla.vim/