No preview for IPython.display.IFrame

This might be related to https://youtrack.jetbrains.com/issue/PY-21447

I have some code plotting a graph with HTML/CSS using the `vis.Network` javascript library. It returns a `IPython.display.IFrame`. In my Jupyter Notebook out, I get a placeholder with `Web: 900 x 426px` but no graph. In the web version, it works. Do you plan to support `IPython.display.IFrame`?

Thank you.