Marc Andreessen has an article that describes how Ning is designed as a "Runtime Environment" just as you have described ~ http://blog.pmarca.com/2007/09/the-three-kinds.html
"... I believe that in the long run, all credible large-scale Internet companies will provide Level 3 platforms. Those that don't won't be competitive with those that do, because those that do will give their users the ability to so easily customize and program as to unleash supernovas of creativity. ..."
It would be a good way for hackers to develop, share, debug Arc code. Boost the language develpment using the pre-release code.
Until we get there, though, may my crawler be let back in? Like I said in email I promise to only restart it after I embed controls over how many URLs I get per hour deeply inside it, and to log my crawling activity and keep an eye on it in future.
The reason I was crawling every few minutes was to get notified of updates to conversations as they happen, before the 'herd' moves on to new feeding grounds. But I can make it crawl even hourly and it'll still allow me to stay kinda abreast of the conversation here.
There's an even better way to do that, which is to let users write little Arc programs to control the way pages are generated. That is the eventual plan.