Your comments

I think this feature would be incredibly useful, basically what the Cmd+R combination does in Textmate - quickly run your code and show the results.

As an alternative, this could be combined with SSH support to run the code on a remote machine instead of using slow-ish web APIs - this would give the advantage of having third-party libs that are installed on the server available, so one can really test code that is more than just a small snippet.