I have a few of their project files so I've seen their scripts ...
the only confusing thing about them using Lua is that majority of them haven't bothered adding comments to their scripts meaning you have to try & figure out what's what by looking at it & then connect the dots to other sections of same script which is spread throughout multiple scripts like for instance their improved walk cycle script.
For mainLoop function I don't add the code itself I just link to another function & if I don't want it to constantly loop I wrap in a small if query.
Have you seen the custom event handler/listener scripts inside of the wiki (on here) that Dundil has been working on - sound promising.
& could you specify what you had in mind for programming interface please on here, pm or even skype

I use "sublime text" myself, which David recommended to me...
In which I create a small include script inside of VS editor to link to the external .lua file I'm working on inside sublime which saves time & then when script i finished I copy/paste into VS. I do agree VS script interface could do with some stuff like line number display & color coded syntax. I'm not expecting all the bells & whistles of sublime though (auto complete & multi-line/word editing & dark background/theme)