There absolutely, positively needs to be the option for default 3D views to display in perspective. This is so fundamental that I would have expected to see these years ago. Having this feature should be one of the biggest priorities for the next release of Revit. It could be a check box or context menu setting on the view cube for the existing default view. I promise it would be game changer and expand the use of Revit for conceptual design as much as technical documentation. Humans see in perspective, so we should be able to work that way too in Revit. Please vote this up! Cheers!