"I suspect that for the most common uses the disadvantages of providing language interoperability in the same process outweigh the advantages"
I've never thought of that. I'm used to using Racket stuff from Arc without hesitation, but then the stuff I use is provided with the Racket language, like parameters and regexes. Most of my non-Arc personal code is in Java or Groovy, and I'm very glad I can use it from Rainbow, but I haven't actually done that yet....
Still, I can personally attest that this kind of feature has played a role in my adoption of languages, regardless of whether I've used it. :)
