This sounds interesting. Can you explain more specifically what you have done? Ideally there would be an Ace Editor syntax highlighter that I could drop in. I will do a little research to see if this exists now in a newer version. If so I can upgrade PlantText.com with it.
Also, I think I found the VIM plugin you are referring to…
https://github.com/aklt/plantuml-syntax
This looks nice. I am going to play with in when I have a minute. Thanks!