For me the artboard should mask to the edge of the page or to the bleed, I don't want to see any content beyond the edge of the artboard on the pasteboard. The Trim preview is not really suitable for working as then I can't see the pasteboard.
Carl, I don’t get it.
You want artboards to be masked, to not show anything outside of them... but at the same time you want to see the contents of the pasteboard, which is just canvas ...the one you want to hide.
So what do you want? Can you please illustrate it?