Maybe this is possible and I just can't figure out how to do it, but it would be super handy if the crop lines of views were "lines" like the outlines of filled regions, masking regions, etc. I know that there are some workarounds using Dynamo to outline viewports, but it seems like it would be simpler to just be able to assign linetypes to the outlines. If you don't want them to show at all (probably default behavior), set them to invisible (or maybe have a toggle not to print them). But for views like interior elevations it would be a huge help to be able to print and control the outline linetype. We often need to outline three sides of an elevation (where the room extends beyond where we need to elevate), so you could just set that side to invisible.
Right now we just draw detail lines over the outline of the viewport to get the dark outline for those views that we need. It's time consuming, doesn't automatically update, and can be a little flaky with the lines sometimes disappearing (I think because Revit doesn't know if they're "inside" or "outside" of the view since they're directly on the outline).
Jason