Currently the Vue Devtools do not recognize vue roots within iframes.

There is work being done on storybook to add Vue compatibility but it uses iframes to wrap the root. vue play uses iframes as well so the devtools only recognize the wrapper application (also built in Vue.) It is also incompatible with tools like jsfiddle.

I think a really cool feature would be to introduce a "context" menu like the one in Chrome Dev Tools:

With this, we could select the context in which we want the Devtools to run. The menu options would include the top level window.document and any iframes it detects one level deeper. When a context is selected, the Devtools will reinitialize. If vue is not discovered within the top-level context, it would default to the first iframe in which it finds a Vue root instance.