If it is going to be as slow as PB.Net, please do not move PB Classic to the VS Shell. We do need some modern features like collapsible code blocks in the editor.
Now that PB has native docking windows, I suggest rewriting the IDE in PowerBuilder. I know that some of it is already PowerBuilder code but it could be rewritten completely in PowerBuilder with a few small parts (DataWindow Painter for example) in C++ as a visual PBNI control.
I would fully support Windows Forms in the PB Classic IDE with direct support of .Net syntax in the code editor instead of the way it is done now where you have to compile the whole app.