It would be nice to be able to manipulate dynamic content directly from the browser: everything is given on the Mathematica-side (CDF, deployment, browser-plugin), and the site would certainly benefit from it: imagine, that new users who just installed Mathematica but have no idea how to use it could immediately try out small programs without copypasting/evaluating them. I realize that SE does not allow the attachment of files to posts (would be useful though in many cases). Perhaps this can be done sometimes?
While I totally support the idea, I have very strong doubts this would ever be possible on SE. Just put yourself in place of SE developers / management: if I were one of them, here are some things that would be a complete no-go:
- Security: since this is based on a plugin, this can affect the client computer in a variety of ways, and SE has no control over it, while full responsibility for it.
- Dependency on external technology, over which SE has no control: the idea is that the posts can stay here for an indefinitely long time and be accessed by new users without problems. If there are some breaking changes introduced in future versions of CDF, this would make older posts broken
I am sure there are other considerations as well.