Great idea.

As some others have pointed out, it may be a bit non-intuitive to see a panel sliding in from the right when you tap a menu entry on the left. Would it be better if the second-level menu “emerged” in situ, or “rose” from below the top-level menu when the menu item was tapped, instead of sliding in from the right? Maybe it’s a matter of taste…

Wonder how soon we will see an Ionic component for this menu type published. :-)