Proprietary VST implementation with many limitations... That is what PC is. I hope CW remove it at some point and replace with normal VST, I mean will merge it with FX Bin. There can be extra (open) interface to provide these "small GUIs" which we have in PC, so VST which want be extra Sonar compatible can use it (I guess other DAWs will follow).
That eliminate all current limitations/problems/wishes. Just think about current FX bin: what is NOT there except small GUIs inside console and inspector? "Flyout" is just normal sized GUI with separate button to show it. Sorry to say, but I have not found any advantages of PC except an overview for the whole chain settings.
BTW In looks like FX Chain is just a micro VST host, or it can be.