It's technically doable, the text in the right pane would be stored as comments in the source. The editor would parse the comments and collapse them into UI ele

It's technically doable, the text in the right pane would be stored as comments in the source. The editor would parse the comments and collapse them into UI elements in the code, so that they could still be copy and pasted e.g. how the little blue capsules in Xcode work. It's a bad idea because it's wasteful of space while achieving very little over a conventional setup.